Bump version to 0.21.0; rework changelog, contributors, and docs

Release:
- Bump version to 0.21.0 and regenerate tusb_option.h, library.json,
  repository.yml, sonar-project.properties, boards.rst, dependencies.rst
- Add 0.21.0 release notes and split the changelog into per-release files
  under docs/info/changelog/ (date out of title, driver/class groups as
  sub-headings, DCD & HCD section after Device/Host stacks)

Contributors:
- Credit each release's PR authors in a Contributors section
- Drop the curated contributors page; add MAINTAINERS.rst

Docs:
- Update Code of Conduct to Contributor Covenant 3.0 (keep it in the repo,
  remove it from the built docs)
- Sidebar: add a home entry, rename the group to "Documentation", move
  Changelog into it, add a GitHub Sponsor button, merge external links,
  rename FAQ; hide the inline toctree on the landing page
- Add the make-release skill and update the AGENTS.md release process

Co-Authored-By: Claude Opus 4.8 (1M context) <[email protected]>

1 files changed, 137 insertions, 62 deletions

diff --git a/CODE_OF_CONDUCT.rst b/CODE_OF_CONDUCT.rst
index 4035c528f..0b143c5b3 100644
--- a/CODE_OF_CONDUCT.rst
+++ b/CODE_OF_CONDUCT.rst
@@ -5,84 +5,159 @@ Code of Conduct
 Our Pledge
 ----------
 
-In the interest of fostering an open and welcoming environment, we as
-contributors and maintainers pledge to making participation in our
-project and our community a harassment-free experience for everyone,
-regardless of age, body size, disability, ethnicity, sex
-characteristics, gender identity and expression, level of experience,
-education, socio-economic status, nationality, personal appearance,
-race, religion, or sexual identity and orientation.
+We pledge to make our community welcoming, safe, and equitable for all.
 
-Our Standards
--------------
+We are committed to fostering an environment that respects and promotes the dignity,
+rights, and contributions of all individuals, regardless of characteristics including
+race, ethnicity, caste, color, age, physical characteristics, neurodiversity,
+disability, sex or gender, gender identity or expression, sexual orientation, language,
+philosophy or religion, national or social origin, socio-economic position, level of
+education, or other status. The same privileges of participation are extended to
+everyone who participates in good faith and in accordance with this Covenant.
 
-Examples of behavior that contributes to creating a positive environment
-include:
+Encouraged Behaviors
+--------------------
 
--  Using welcoming and inclusive language
--  Being respectful of differing viewpoints and experiences
--  Gracefully accepting constructive criticism
--  Focusing on what is best for the community
--  Showing empathy towards other community members
+While acknowledging differences in social norms, we all strive to meet our community's
+expectations for positive behavior. We also understand that our words and actions may be
+interpreted differently than we intend based on culture, background, or native language.
 
-Examples of unacceptable behavior by participants include:
+With these considerations in mind, we agree to behave mindfully toward each other and act
+in ways that center our shared values, including:
 
--  The use of sexualized language or imagery and unwelcome sexual
-   attention or advances
--  Trolling, insulting/derogatory comments, and personal or political
-   attacks
--  Public or private harassment
--  Publishing others' private information, such as a physical or
-   electronic address, without explicit permission
--  Other conduct which could reasonably be considered inappropriate in a
-   professional setting
+1. Respecting the **purpose of our community**, our activities, and our ways of gathering.
+2. Engaging **kindly and honestly** with others.
+3. Respecting **different viewpoints** and experiences.
+4. **Taking responsibility** for our actions and contributions.
+5. Gracefully giving and accepting **constructive feedback**.
+6. Committing to **repairing harm** when it occurs.
+7. Behaving in other ways that promote and sustain the **well-being of our community**.
 
-Our Responsibilities
+Restricted Behaviors
 --------------------
 
-Project maintainers are responsible for clarifying the standards of
-acceptable behavior and are expected to take appropriate and fair
-corrective action in response to any instances of unacceptable behavior.
+We agree to restrict the following behaviors in our community. Instances, threats, and
+promotion of these behaviors are violations of this Code of Conduct.
 
-Project maintainers have the right and responsibility to remove, edit,
-or reject comments, commits, code, wiki edits, issues, and other
-contributions that are not aligned to this Code of Conduct, or to ban
-temporarily or permanently any contributor for other behaviors that they
-deem inappropriate, threatening, offensive, or harmful.
+1. **Harassment.** Violating explicitly expressed boundaries or engaging in unnecessary
+   personal attention after any clear request to stop.
+2. **Character attacks.** Making insulting, demeaning, or pejorative comments directed at
+   a community member or group of people.
+3. **Stereotyping or discrimination.** Characterizing anyone's personality or behavior on
+   the basis of immutable identities or traits.
+4. **Sexualization.** Behaving in a way that would generally be considered inappropriately
+   intimate in the context or purpose of the community.
+5. **Violating confidentiality.** Sharing or acting on someone's personal or private
+   information without their permission.
+6. **Endangerment.** Causing, encouraging, or threatening violence or other harm toward
+   any person or group.
+7. Behaving in other ways that **threaten the well-being** of our community.
 
-Scope
------
+Other Restrictions
+~~~~~~~~~~~~~~~~~~
 
-This Code of Conduct applies both within project spaces and in public
-spaces when an individual is representing the project or its community.
-Examples of representing a project or community include using an
-official project e-mail address, posting via an official social media
-account, or acting as an appointed representative at an online or
-offline event. Representation of a project may be further defined and
-clarified by project maintainers.
+1. **Misleading identity.** Impersonating someone else for any reason, or pretending to be
+   someone else to evade enforcement actions.
+2. **Failing to credit sources.** Not properly crediting the sources of content you
+   contribute.
+3. **Promotional materials.** Sharing marketing or other commercial content in a way that
+   is outside the norms of the community.
+4. **Irresponsible communication.** Failing to responsibly present content which includes,
+   links or describes any other restricted behaviors.
 
-Enforcement
------------
+Reporting an Issue
+------------------
+
+Tensions can occur between community members even when they are trying their best to
+collaborate. Not every conflict represents a code of conduct violation, and this Code of
+Conduct reinforces encouraged behaviors and norms that can help avoid conflicts and
+minimize harm.
+
+When an incident does occur, it is important to report it promptly. To report a possible
+violation, contact the project team at [email protected].
+
+Community Moderators take reports of violations seriously and will make every effort to
+respond in a timely manner. They will investigate all reports of code of conduct
+violations, reviewing messages, logs, and recordings, or interviewing witnesses and other
+participants. Community Moderators will keep investigation and enforcement actions as
+transparent as possible while prioritizing safety and confidentiality. In order to honor
+these values, enforcement actions are carried out in private with the involved parties,
+but communicating to the whole community may be part of a mutually agreed upon resolution.
+
+Addressing and Repairing Harm
+-----------------------------
+
+If an investigation by the Community Moderators finds that this Code of Conduct has been
+violated, the following enforcement ladder may be used to determine how best to repair
+harm, based on the incident's impact on the individuals involved and the community as a
+whole. Depending on the severity of a violation, lower rungs on the ladder may be skipped.
+
+1. **Warning**
+
+   - **Event:** A violation involving a single incident or series of incidents.
+   - **Consequence:** A private, written warning from the Community Moderators.
+   - **Repair:** Examples of repair include a private written apology, acknowledgement of
+     responsibility, and seeking clarification on expectations.
 
-Instances of abusive, harassing, or otherwise unacceptable behavior may
-be reported by contacting the project team at [email protected]. All
-complaints will be reviewed and investigated and will result in a
-response that is deemed necessary and appropriate to the circumstances.
-The project team is obligated to maintain confidentiality with regard to
-the reporter of an incident. Further details of specific enforcement
-policies may be posted separately.
+2. **Temporarily Limited Activities**
 
-Project maintainers who do not follow or enforce the Code of Conduct in
-good faith may face temporary or permanent repercussions as determined
-by other members of the project's leadership.
+   - **Event:** A repeated incidence of a violation that previously resulted in a warning,
+     or the first incidence of a more serious violation.
+   - **Consequence:** A private, written warning with a time-limited cooldown period
+     designed to underscore the seriousness of the situation and give the community members
+     involved time to process the incident. The cooldown period may be limited to particular
+     communication channels or interactions with particular community members.
+   - **Repair:** Examples of repair may include making an apology, using the cooldown period
+     to reflect on actions and impact, and being thoughtful about re-entering community
+     spaces after the period is over.
+
+3. **Temporary Suspension**
+
+   - **Event:** A pattern of repeated violation which the Community Moderators have tried to
+     address with warnings, or a single serious violation.
+   - **Consequence:** A private written warning with conditions for return from suspension.
+     In general, temporary suspensions give the person being suspended time to reflect upon
+     their behavior and possible corrective actions.
+   - **Repair:** Examples of repair include respecting the spirit of the suspension, meeting
+     the specified conditions for return, and being thoughtful about how to reintegrate with
+     the community when the suspension is lifted.
+
+4. **Permanent Ban**
+
+   - **Event:** A pattern of repeated code of conduct violations that other steps on the
+     ladder have failed to resolve, or a violation so serious that the Community Moderators
+     determine there is no way to keep the community safe with this person as a member.
+   - **Consequence:** Access to all community spaces, tools, and communication channels is
+     removed. In general, permanent bans should be rarely used, should have strong reasoning
+     behind them, and should only be resorted to if working through other remedies has failed
+     to change the behavior.
+   - **Repair:** There is no possible repair in cases of this severity.
+
+This enforcement ladder is intended as a guideline. It does not limit the ability of
+Community Managers to use their discretion and judgment, in keeping with the best interests
+of our community.
+
+Scope
+-----
+
+This Code of Conduct applies within all community spaces, and also applies when an
+individual is officially representing the community in public or other spaces. Examples of
+representing our community include using an official email address, posting via an official
+social media account, or acting as an appointed representative at an online or offline event.
 
 Attribution
 -----------
 
-This Code of Conduct is adapted from the `Contributor
-Covenant <https://www.contributor-covenant.org>`__, version 1.4,
-available at
-https://www.contributor-covenant.org/version/1/4/code-of-conduct.html
+This Code of Conduct is adapted from the Contributor Covenant, version 3.0, permanently
+available at https://www.contributor-covenant.org/version/3/0/.
+
+Contributor Covenant is stewarded by the Organization for Ethical Source and licensed under
+CC BY-SA 4.0. To view a copy of this license, visit
+https://creativecommons.org/licenses/by-sa/4.0/.
 
-For answers to common questions about this code of conduct, see
-https://www.contributor-covenant.org/faq
+For answers to common questions about Contributor Covenant, see the FAQ at
+https://www.contributor-covenant.org/faq. Translations are provided at
+https://www.contributor-covenant.org/translations. Additional enforcement and community
+guideline resources can be found at https://www.contributor-covenant.org/resources. The
+enforcement ladder was inspired by the work of
+`Mozilla's code of conduct team <https://github.com/mozilla/inclusion>`__.