build: add the ESP32-C5

The C5 builds like the C6: a debug build with one 3 MB app slot, so it
updates over USB. At CORE_DEBUG_LEVEL=2 its image left 3.4 KB of the
1.5 MB OTA slot, under CI's 8 KB.

- platformio.ini: env esp32c5 (esp32-c5-devkitc-1).
- Chip model "c5", so the updater and releases name its files
  SomfyController.*.esp32c5.bin.
- Radio defaults: the framework's SPI pins (CSN 6, MOSI 8, MISO 9,
  SCK 10), TX 4, RX 5.
- Web UI: GPIO 0-28, without 13-14 (USB) and 15-22 (flash, PSRAM).
- CI builds and releases it; its bootloader sits at 0x2000.
- ADR 0003: amended.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/ConfigSettings.cpp

@@ -134,6 +134,11 @@ bool ConfigSettings::begin() {
     case esp_chip_model_t::CHIP_ESP32C3:
       strcpy(this->chipModel, "c3");
       break;
+    #ifdef CONFIG_IDF_TARGET_ESP32C5
+    case esp_chip_model_t::CHIP_ESP32C5:
+      strcpy(this->chipModel, "c5");
+      break;
+    #endif
     #ifdef CONFIG_IDF_TARGET_ESP32C6
     case esp_chip_model_t::CHIP_ESP32C6:
       strcpy(this->chipModel, "c6");