feat: ESP32-C3 Super Mini target, GoPro link fix, DJI Action 2 support

[miszczuq]

Add a second board target and a new camera backend, and fix the GoPro link being dropped right after it connects.

ESP32-C3 Super Mini (new esp32c3-supermini env)

• platformio.ini: shared settings moved to [env]; new env on the nologo_esp32c3_super_mini board (ESP32-C3FH4: 4 MB flash, no PSRAM, USB-Serial/JTAG). The esp32s3-zero env builds as before.
• config.h: per-board pin maps selected by a BOARD_* define. C3: FC UART on GPIO20 (RX) / GPIO21 (TX), status LED on GPIO8.
• StatusLed: support a plain single-colour LED (the C3 board has a blue active-low LED instead of a WS2812); states are told apart by blink pattern: slow blink = searching, double flash = config Wi-Fi client, solid = camera connected, fast blink = recording.
• main.cpp: on single-core chips loop() blocks for a tick so the camera task and the idle task are not starved.
• README: build, flash and wiring notes for the C3 board.

GoPro

• Fix the link being dropped as "stale" right after connecting: the check used a timestamp taken before the blocking status/setting writes, so a reply landing during them made now - lastUpdateMs underflow.
• Log the NimBLE error code when a connect attempt fails.

DJI Action 2 (new "DJI Action 2" camera type)

• New DjiAction2Camera backend: DUML over BLE with the app-level pairing the Mimo app uses (01 00 arm write to FFF4, 0x07/0x45 pairing request, ACK of the on-screen approval), record start/stop via 0x02/0x02. Pairing flow ported from shutterlink (MIT).
• The camera sends no telemetry once paired, so the BLE link itself is the liveness signal and record state/time come from our own commands. Photo capture, mode switch, SD free, time left and resolution are unavailable.
• Web UI: new camera type in the bind wizard; every DJI camera is listed for each DJI type (the scan can't tell an Action 2 apart); OSD fields and channel functions the Action 2 can't provide are hidden.

Tested on an ESP32-C3 Super Mini:

• flashes and boots, Wi-Fi AP and Web UI work
• GoPro HERO12 pairs and stays connected with live status
• DJI Action 2 pairs; link stability after the liveness change and record start/stop not verified yet
• not yet tested with a flight controller (MSP, OSD, record on arm)