Migrate all ESP32 envs to Arduino-ESP32 3.x (pioarduino)

The registry espressif32 platform still ships Arduino core 2.0.17, which
lacks ESP32-C6 support. Switch every ESP32 env to the pioarduino fork
(Arduino-ESP32 3.x) via a shared ${common.platform_esp32} variable and
consolidate shared settings into [env].

Rewrite the PWM code for the 3.x LEDC API:
- ledcSetup + ledcAttachPin -> ledcAttach(pin, freq, res)
- ledcDetachPin -> ledcDetach
- ledcWrite now addresses PWM by pin instead of channel index

Adds the esp32-c6-devkitc-1 env; all four ESP32 envs build clean.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

platformio.ini

@@ -8,37 +8,43 @@
 ; Please visit documentation for the other options and examples
 ; https://docs.platformio.org/page/projectconf.html
 
+[common]
+; All ESP32 targets use the pioarduino fork, which ships Arduino-ESP32 3.x
+; (the registry espressif32 platform is still on 2.0.17 and lacks C6 support).
+platform_esp32 = https://github.com/pioarduino/platform-espressif32/releases/download/55.03.39/platform-espressif32.zip
+
 [env]
+framework = arduino
+monitor_speed = 115200
+lib_deps =
+    tzapu/WiFiManager@^2.0.17
+    bblanchon/ArduinoJson@^7.4.3
+    knolleary/PubSubClient@^2.8
 
 [env:esp32-s3-devkitc-1]
-platform = espressif32
+platform = ${common.platform_esp32}
 board = esp32-s3-devkitc-1
-framework = arduino
-monitor_speed = 115200
 board_build.filesystem = littlefs
-lib_deps =
-    tzapu/WiFiManager@^2.0.17
-    bblanchon/ArduinoJson@^7.0.0
-    knolleary/PubSubClient@^2.8
 
 [env:esp32dev]
+platform = ${common.platform_esp32}
 board = esp32dev
-framework = arduino
-platform = espressif32
-monitor_speed = 115200
 board_build.filesystem = littlefs
-lib_deps =
-    tzapu/WiFiManager@^2.0.17
-    bblanchon/ArduinoJson@^7.4.3
-    knolleary/PubSubClient@^2.8
 
 [env:esp32-C3-devkitm-1]
+platform = ${common.platform_esp32}
 board = esp32-c3-devkitm-1
-framework = arduino
-platform = espressif32
-monitor_speed = 115200
 board_build.filesystem = littlefs
-lib_deps =
-    tzapu/WiFiManager@^2.0.17
-    bblanchon/ArduinoJson@^7.4.3
-    knolleary/PubSubClient@^2.8
+
+[env:esp32-c6-devkitc-1]
+platform = ${common.platform_esp32}
+board = esp32-c6-devkitc-1
+board_build.filesystem = littlefs
+
+[env:rpipico2w]
+; RP2350 support requires the maxgerhardt fork of the raspberrypi platform
+; and the earlephilhower arduino-pico core.
+platform = https://github.com/maxgerhardt/platform-raspberrypi.git
+board = rpipico2w
+board_build.core = earlephilhower
+board_build.filesystem_size = 0.5m