Add chip temperature sensor and RGB LED control, verified live in HA

Quick end-to-end data-flow proof using only what's on the ESP32-C6-
DevKitC-1 itself (no sensors on the bare devkit -- confirmed via
research: BOOT button, WS2812 LED, no external sensors):

- drivers::chip_temperature_* wraps ESP-IDF's built-in
  temperature_sensor driver (SoC die temperature).
- drivers::rgb_led_* wraps the onboard WS2812 (GPIO8) via the
  espressif/led_strip managed component (another external registry
  dependency, like mdns/mqtt).
- profiles::ChipTemperatureSensor is the first real implementation of
  the Sensor interface designed earlier, converting the driver's float
  reading to the fixed-point convention once at the boundary.
- transport/mqtt.cpp publishes chip temperature as an HA "temperature"
  sensor every 30s, and exposes the LED as an HA "light" entity
  (rgb_command_topic) -- the first use of MQTT subscribe in this
  project, not just publish.

Added a ChipTemperature SensorChannel (distinct from
AmbientTemperature -- different meaning/range) to sensor.h.

Verified live: both the chip temperature reading and LED color control
work from Home Assistant against the real device.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

components/profiles/README.md

@@ -1,3 +1,7 @@
 # profiles
 
 Exposes reusable sensor/actuator capabilities (reed switch, hall sensor, push button, pulse counter, analog input, DS18B20, BME280, leak sensor, PIR, generic I2C device) to the Lua runtime, backed by `sensors`. `REQUIRES sensors`.
+
+Concrete `Sensor` implementations live here (not in `sensors`, which owns the shared interface/types), and reach down to `drivers` directly for the actual hardware access -- `sensors` is the shared contract, not a mandatory pass-through. `REQUIRES drivers` too.
+
+- `ChipTemperatureSensor` (`include/chip_temperature_sensor.h`) -- the first real `Sensor` implementation, wrapping `drivers::chip_temperature_*` (the ESP32-C6's internal die temperature). Added to get real data flowing end-to-end (drivers -> profiles -> transport/MQTT) before more sensor types exist.