Firmware v2.1.9

Fix: BLE END packet delivery

Problem: ~60% of PTT recordings were silently lost because the END packet (which tells the phone to process the recording) failed to send — the BLE TX buffers were exhausted by audio data packets at the moment of button release.

Fix: Instead of sending the END packet directly from the button handler (competing with the audio pusher thread for BLE TX buffers), the END packet is now enqueued into the same ring buffer as audio frames. The pusher thread sends it naturally after all remaining audio data — no competition, no lost recordings.

Changed files

• firmware/pinclaw_zephyr/src/transport.h — added enqueue_end_packet()
• firmware/pinclaw_zephyr/src/transport.c — implemented enqueue_end_packet()
• firmware/pinclaw_zephyr/src/button.c — button release uses ring buffer instead of direct BLE notify