fix: address PR review feedback for MIDI 2.0 drivers

Host driver (midi2_host.c):
- midih2_open() now returns actual parsed length instead of max_len,
  preventing composite device interface conflicts
- Parsers (alt0/alt1) refactored to return const uint8_t* end pointer
  following midi_host.c switch/case pattern
- Alt 1 CS Endpoint now parses MIDI 2.0 layout (bNumGrpTrmBlk at
  offset 3 with MIDI_CS_ENDPOINT_GENERAL_2_0 subtype check) instead
  of reusing MIDI 1.0 struct (bNumEmbMIDIJack)
- midih2_set_config() now issues SET_INTERFACE control request via
  tuh_interface_set() before completing configuration. Falls back to
  alt 0 if SET_INTERFACE fails
- Extracted midih2_set_config_complete() and midih2_set_interface_cb()
  for async SET_INTERFACE handling

Device driver (midi2_device.c):
- midi2d_open() skip loop now checks bInterfaceNumber, stopping at
  interfaces that belong to other functions in composite devices
- SET_INTERFACE handler now rejects alt > 1 (returns false/stall)
- Named constants for GTB descriptor types and MIDI protocol values

Descriptor macros (usbd.h):
- TUD_MIDI2_DESC_ALT1_HEAD: iInterface set to 0 (consistent with
  Alt 0), wTotalLength now uses TUD_MIDI2_DESC_ALT1_CS_LEN to cover
  all Alt 1 class-specific descriptors
- TUD_MIDI2_DESC_ALT1_EP: now accepts GTB ID list via variadic args,
  emitting complete CS endpoint descriptor

Host example:
- CMakeLists.txt restricted to rp2040 family (display.c requires
  Pico SDK headers)
- display.c: null terminator after strncpy in log scroll

Documentation:
- class_drivers.rst updated to reflect SET_INTERFACE behavior and
  auto-select with fallback

Addresses: Codex P1 (#1, #2, #3), Copilot (#4-#9)

2 files changed, 3 insertions, 1 deletions

diff --git a/examples/host/midi2_host/CMakeLists.txt b/examples/host/midi2_host/CMakeLists.txt
index 221de7adf..cd70d122a 100644
--- a/examples/host/midi2_host/CMakeLists.txt
+++ b/examples/host/midi2_host/CMakeLists.txt
@@ -6,7 +6,8 @@ project(midi2_host C CXX ASM)
 
 family_initialize_project(${PROJECT_NAME} ${CMAKE_CURRENT_LIST_DIR})
 
-if(FAMILY STREQUAL "espressif")
+# This example requires PIO-USB and Pico SDK (I2C, SSD1306 display)
+if(NOT FAMILY STREQUAL "rp2040")
   return()
 endif()
 
diff --git a/examples/host/midi2_host/src/display.c b/examples/host/midi2_host/src/display.c
index 6d81bcd5c..4745c2961 100644
--- a/examples/host/midi2_host/src/display.c
+++ b/examples/host/midi2_host/src/display.c
@@ -190,6 +190,7 @@ void display_log(const char* text, uint16_t color) {
   if (log_count >= LOG_LINES) {
     for (int i = 0; i < LOG_LINES - 1; i++) {
       strncpy(log_lines[i], log_lines[i + 1], CHARS_PER_LINE);
+      log_lines[i][CHARS_PER_LINE] = '\0';
     }
     log_count = LOG_LINES - 1;
   }