build: move to pioarduino 55.03.312 (Arduino 3.3.12, ESP-IDF 5.5)

IDF 4.4 gets no more security fixes, and the planned RMT radio needs
IDF 5's RMT driver.  See docs/adr/0003-pioarduino-idf55.md.

- Every env on one pinned pioarduino release.  C6 drops its own
  library list and flags but stays a debug build on huge_app.
- Release envs build at CORE_DEBUG_LEVEL=2 so the ESP32 image fits its
  1.5 MB OTA slot (17 KB free); debug envs stay at 3.
- Drop the C3: its image is 76.5 KB over the OTA slot on IDF 5.5.
- CI installs pioarduino's Core and checks firmware.bin against the app
  partition, failing under 8 KB free.  PlatformIO's "Flash:" figure
  reads ~45 KB low and passed a C3 image that doesn't fit.
- esp_task_wdt_reconfigure(): on 3.x the core already starts the watchdog
  and esp_task_wdt_init() fails, so the C6 build kept the 5 s default.
- An updated firmware is kept only once it has run 60 s with the
  network up; a reset before then rolls back to the previous one.
- ETH.begin() takes the 3.x argument order; Arduino 2.x branches gone.

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

platformio.ini

@@ -15,7 +15,9 @@ src_dir = src
 ; Shared by every firmware env (they extend it).  Kept out of [env] so the
 ; native test env doesn't inherit the Arduino framework and ESP32 libraries.
 [esp32]
-platform =  espressif32 @ 6.13.0
+; pioarduino: Arduino 3.3.12 on ESP-IDF 5.5.  Pinned to a release so an
+; upgrade is its own PR (docs/adr/0003-pioarduino-idf55.md).
+platform = https://github.com/pioarduino/platform-espressif32/releases/download/55.03.312/platform-espressif32.zip
 framework = arduino
 ; Unit tests only run on the PC: pio test -e native
 test_ignore = *
@@ -30,8 +32,9 @@ extra_scripts =
 	pre:minify.py
 	post:archive_elf.py
 board_build.filesystem = littlefs
-build_flags = 
-	-DCORE_DEBUG_LEVEL=3
+; Each env adds a CORE_DEBUG_LEVEL: 2 (warnings) for release builds, which
+; only fit the 1.5 MB OTA slot without the info logs, 3 for debug builds.
+build_flags =
 	-DCONFIG_ESP_COREDUMP_ENABLE_TO_FLASH=1
 	-DCONFIG_ESP_COREDUMP_DATA_FORMAT_ELF=1
 	-DCONFIG_ESP_COREDUMP_CHECKSUM_CRC32=1
@@ -57,7 +60,9 @@ build_flags =
 extends = esp32
 board = esp32dev
 board_build.partitions = esp32_3MB.csv
-build_flags = ${dualcore.build_flags}
+build_flags =
+	${dualcore.build_flags}
+	-DCORE_DEBUG_LEVEL=2
 
 [env:esp32devdbg]
 extends = esp32
@@ -73,39 +78,26 @@ board_build.partitions = esp32_huge_app.csv
 ; KBs of flash per file, so treat every file as large.
 build_flags =
 	${dualcore.build_flags}
+	-DCORE_DEBUG_LEVEL=3
 	--param=large-unit-insns=1000
 
-[env:esp32c3]
-extends = esp32
-board = esp32-c3-devkitm-1
-board_build.partitions = esp32_3MB.csv
-
 [env:esp32s3]
 extends = esp32
 board = esp32-s3-devkitc-1
-build_flags = ${dualcore.build_flags}
+build_flags =
+	${dualcore.build_flags}
+	-DCORE_DEBUG_LEVEL=2
 
+; Released as a debug build with one 3 MB app slot, so C6 boards update over
+; USB, not OTA.
 [env:esp32c6]
 extends = esp32
-platform = https://github.com/pioarduino/platform-espressif32/releases/download/stable/platform-espressif32.zip
 board = seeed_xiao_esp32c6
 build_type = debug
 board_build.partitions = esp32_huge_app.csv
 build_flags =
 	${esp32.build_flags}
-	-DCONFIG_FREERTOS_HZ=1000
-	-include "driver/gpio.h"
-lib_deps = 
-	; Low-Level libs, frameowrks and drivers
-	ESP32Async/AsyncTCP
-	https://github.com/Viproz/SmartRC-CC1101-Driver-Lib.git
-	; Commmunication Protocol
-	links2004/WebSockets
-	https://github.com/hmueller01/pubsubclient3.git
-	; Data-Parsing
-	bblanchon/ArduinoJson
-	; High-level wrappers/servers
-	ESP32Async/ESPAsyncWebServer
+	-DCORE_DEBUG_LEVEL=3
 
 ; Host-side unit tests: pio test -e native  (needs gcc/g++ on PATH).
 ; Only the sources the tests cover are built; test/stubs stands in for Arduino.h.