Add app_controller wiring UART, integration, status monitor and Zigbee
ZCL layers together with command/feedback flows and reset/recovery.
Add main.c entry point (guarded for test builds), app_controller_test
integration tests (full command cycle, timing under load, recovery),
Makefile target, and Readme updates.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>