docs: add build-doc tooling and a README for every example

Documentation tooling:
- Add the `build-doc` skill and `tools/build_doc.py` wrapper for local
  Sphinx builds (clean / -W / open).
- Enable Markdown (MyST) in conf.py and auto-collect
  examples/{device,host,dual}/*/README.md into a 3-level Examples nav
  (Examples > Device/Host/Dual > example), noting each page's source
  location and normalizing headings to a single H1.
- Remove the stale `.claude/commands/build-doc.md`; point the AGENTS.md
  Documentation section at the skill.

Example docs:
- Add a README.md for every device/host/dual example: what it does, USB
  interface table, notable tusb_config.h settings, generic CMake + Make
  build steps, and how to try it.
- Fold each *_freertos variant into its base README, noting the FreeRTOS
  source path and any RTOS-specific behavior.

Generated docs/examples/ output is git-ignored. Builds clean with
`sphinx-build -W`.

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

1 files changed, 14 insertions, 1 deletions

diff --git a/examples/device/printer_to_cdc/README.md b/examples/device/printer_to_cdc/README.md
index ecb9a678f..efba70ffb 100644
--- a/examples/device/printer_to_cdc/README.md
+++ b/examples/device/printer_to_cdc/README.md
@@ -7,13 +7,26 @@ This example demonstrates a USB composite device with a Printer class interface
 
 This is useful for debugging printer class communication or as a reference for implementing printer class devices.
 
-#### USB Interfaces
+#### USB Descriptors
 
 | Interface | Class | Description |
 |-----------|-------|-------------|
 | 0 | CDC ACM | Virtual serial port |
 | 2 | Printer | USB Printer (bidirectional, protocol 2) |
 
+#### Configuration
+
+Notable `tusb_config.h` settings:
+
+```c
+#define CFG_TUD_CDC                1
+#define CFG_TUD_PRINTER            1
+#define CFG_TUD_CDC_RX_BUFSIZE     (TUD_OPT_HIGH_SPEED ? 512 : 64)
+#define CFG_TUD_CDC_TX_BUFSIZE     (TUD_OPT_HIGH_SPEED ? 512 : 64)
+#define CFG_TUD_PRINTER_RX_BUFSIZE (TUD_OPT_HIGH_SPEED ? 512 : 64)
+#define CFG_TUD_PRINTER_TX_BUFSIZE (TUD_OPT_HIGH_SPEED ? 512 : 64)
+```
+
 #### How to Test
 
 The device exposes two endpoints on the host: