feat: end-to-end app controller integration and tests

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>

Readme.md

@@ -13,6 +13,7 @@ This project implements a bridge between Zigbee (Home Assistant) and UART-based
 - Bidirectional communication between Zigbee and UART layers
 - Status monitoring with periodic AC polling, fault detection, and a communication watchdog
 - Configurable timing controls (50ms command spacing)
+- End-to-end application controller wiring all layers together with reset/recovery
 
 ## Directory Structure
 
@@ -23,6 +24,7 @@ src/
   zigbee_zcl.c/h       - Zigbee ZCL Thermostat cluster
   integration_layer.c/h- Integration between Zigbee and UART layers
   status_monitor.c/h   - AC status polling, fault detection, and comms watchdog
+  app_controller.c/h   - End-to-end controller wiring all layers + reset/recovery
   main.c               - Application entry point
 
 test/
@@ -31,6 +33,7 @@ test/
   zigbee_zcl_test.c           - Unit tests for Zigbee ZCL
   integration_layer_test.c    - Unit tests for integration layer
   status_monitor_test.c       - Unit tests for status monitoring
+  app_controller_test.c       - End-to-end integration tests (full command cycles)
 
 docs/
   protocol.md                 - MideaUART protocol details
@@ -81,6 +84,36 @@ The `status_monitor` module (see `src/status_monitor.c/h`) provides:
 Configuration (`status_monitor_config_t`) exposes `poll_interval_ms` (default
 5000ms), `timeout_ms` (default 1000ms), and `max_retries` (default 3).
 
+## End-to-End Integration
+
+The `app_controller` module (see `src/app_controller.c/h`) ties every layer
+together and drives the two full data flows:
+
+- Command path (HA → Zigbee → Integration → UART → AC):
+  `app_controller_process_zigbee_command()` forwards an incoming Zigbee command
+  through the integration layer, which encodes and transmits the corresponding
+  MideaUART frame with 50ms rate limiting.
+- Feedback path (AC → UART → Status → Integration → Zigbee → HA):
+  `app_controller_process_ac_status()` decodes a MideaUART status frame, runs
+  fault detection / watchdog bookkeeping, and publishes the result to the ZCL
+  Thermostat cluster for Home Assistant to read.
+
+Reset and recovery:
+
+- `app_controller_reset()` re-initializes UART and integration state and clears
+  status-monitor error counters without dropping configuration.
+- `app_controller_recover_if_needed()` performs a reset automatically when the
+  communication watchdog trips (retries exhausted or poll window exceeded).
+- `app_controller_is_healthy()` reports comms liveness plus fault state.
+
+`src/main.c` provides the firmware entry point and service loop. Its `main()` is
+compiled only for the firmware build; unit-test binaries define `UNIT_TEST` and
+supply their own `main()`.
+
+Integration tests in `test/app_controller_test.c` exercise full command cycles,
+including a HA→…→AC→…→HA round trip, timing under a 100-command burst, and the
+reset/recovery paths.
+
 ## Implementation Progress
 
 See `docs/plans/2026-07-05-ballu-ac-esp32c6-controller-implementation.md` for detailed implementation plan and progress tracking.