Split function keys from HID path

docs/firmware_proto_transport.md

@@ -36,3 +36,26 @@ Design notes:
 - CDC transport module
 - GATT transport module
 - nanopb integration and generated protocol code
+
+### Node 2: keyboard split point
+
+Files updated in this step:
+
+- `src/modules/keyboard_module.c`
+
+Design notes:
+
+- reuse the existing keymap and HID path
+- add one explicit split point before HID submission
+- keep normal keys on HID
+- send configured function keys to private transport only
+
+Implemented behavior:
+
+- store the 29-byte function bitmap
+- for keyboard usages marked as function keys:
+  - stop normal HID reporting
+  - emit `function_key_event`
+- for consumer usages marked as function keys:
+  - stop normal HID reporting
+  - emit `function_key_event`