serial_bridge.c + .h:
- Implement 20pkt/s throttle with 240-byte buffer
- serial_bridge_on_usb_data() for buffering USB serial data
- Flush every 50ms or 500ms stale timeout
led_button.c + .h:
- Per-color LED blink toggle in led_button_tick()
- BLUE_BLINK 200ms, RED_BLINK 100ms, GREEN_BLINK 200ms
- Fix: was set_led(true,true,true) for all blink patterns
main.c:
- Route USB serial data through serial_bridge_on_usb_data
- Add led_button_tick() call in main loop
state_machine.c:
- Add binary_parser_reset() on SERIAL_BRIDGE re-deploy
