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/drivers/src/chip_temperature.cpp

@@ -0,0 +1,37 @@
+#include "chip_temperature.h"
+
+#include "driver/temperature_sensor.h"
+#include "esp_log.h"
+
+namespace kvida::drivers {
+
+namespace {
+constexpr const char *TAG = "chip_temperature";
+temperature_sensor_handle_t g_handle = nullptr;
+} // namespace
+
+void chip_temperature_init()
+{
+    if (g_handle) {
+        return;
+    }
+    temperature_sensor_config_t cfg = TEMPERATURE_SENSOR_CONFIG_DEFAULT(-10, 80);
+    ESP_ERROR_CHECK(temperature_sensor_install(&cfg, &g_handle));
+    ESP_ERROR_CHECK(temperature_sensor_enable(g_handle));
+}
+
+float chip_temperature_read_celsius()
+{
+    if (!g_handle) {
+        ESP_LOGE(TAG, "chip_temperature_read_celsius() called before chip_temperature_init()");
+        return 0.0f;
+    }
+    float celsius = 0.0f;
+    esp_err_t err = temperature_sensor_get_celsius(g_handle, &celsius);
+    if (err != ESP_OK) {
+        ESP_LOGW(TAG, "temperature_sensor_get_celsius failed: %s", esp_err_to_name(err));
+    }
+    return celsius;
+}
+
+} // namespace kvida::drivers

components/drivers/src/rgb_led.cpp

@@ -0,0 +1,47 @@
+#include "rgb_led.h"
+
+#include "esp_log.h"
+#include "led_strip.h"
+
+namespace kvida::drivers {
+
+namespace {
+constexpr const char *TAG = "rgb_led";
+constexpr int kGpio = 8; // WS2812 on ESP32-C6-DevKitC-1
+led_strip_handle_t g_strip = nullptr;
+} // namespace
+
+void rgb_led_init()
+{
+    if (g_strip) {
+        return;
+    }
+
+    led_strip_config_t strip_config = {};
+    strip_config.strip_gpio_num = kGpio;
+    strip_config.max_leds = 1;
+    strip_config.led_model = LED_MODEL_WS2812;
+    strip_config.color_component_format = LED_STRIP_COLOR_COMPONENT_FMT_GRB;
+
+    led_strip_rmt_config_t rmt_config = {};
+    rmt_config.resolution_hz = 10 * 1000 * 1000;
+
+    esp_err_t err = led_strip_new_rmt_device(&strip_config, &rmt_config, &g_strip);
+    if (err != ESP_OK) {
+        ESP_LOGE(TAG, "led_strip_new_rmt_device failed: %s", esp_err_to_name(err));
+        return;
+    }
+    led_strip_clear(g_strip);
+}
+
+void rgb_led_set_color(uint8_t red, uint8_t green, uint8_t blue)
+{
+    if (!g_strip) {
+        ESP_LOGE(TAG, "rgb_led_set_color() called before rgb_led_init()");
+        return;
+    }
+    led_strip_set_pixel(g_strip, 0, red, green, blue);
+    led_strip_refresh(g_strip);
+}
+
+} // namespace kvida::drivers