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/src/chip_temperature_sensor.cpp

@@ -0,0 +1,36 @@
+#include "chip_temperature_sensor.h"
+
+#include "chip_temperature.h"
+
+namespace kvida {
+
+void ChipTemperatureSensor::begin()
+{
+    drivers::chip_temperature_init();
+}
+
+bool ChipTemperatureSensor::fetch()
+{
+    float celsius = drivers::chip_temperature_read_celsius();
+
+    // Convert to the fixed-point convention (val1 + val2 * 1e-6) once, at
+    // the boundary where the underlying driver hands us a float --
+    // ESP32-C6 has no hardware FPU, see sensor.h.
+    auto val1 = static_cast<int32_t>(celsius);
+    auto val2 = static_cast<int32_t>((celsius - static_cast<float>(val1)) * 1000000.0f);
+
+    last_ = SensorValue{val1, val2, "C", 0};
+    fetched_ = true;
+    return true;
+}
+
+bool ChipTemperatureSensor::get(SensorChannel channel, SensorValue &out)
+{
+    if (!fetched_ || channel != SensorChannel::ChipTemperature) {
+        return false;
+    }
+    out = last_;
+    return true;
+}
+
+} // namespace kvida