Adds a LEDManager class (src/helpers/ui/LEDManager.h) that centralizes
all LED control into one component with begin()/loop() lifecycle and
per-pin active-HIGH/LOW polarity support.
LED settings are exposed as custom vars (led.status, led.activity)
accessible via companion radio binary protocol, CLI set/get commands,
and the SensorManager settings interface.
Status LED modes: off, boot-30s, slow blink (200ms/4s), always on.
Activity LED modes: off, BLE only, LoRa TX only, BLE + LoRa TX.
Integrated into 23 board variants, replacing scattered hardcoded
digitalWrite calls in onBeforeTransmit/onAfterTransmit/powerOff.
Enable GPS time synchronization across all variants by passing
&rtc_clock to MicroNMEALocationProvider. When GPS gets a valid
fix, the RTC clock is now updated automatically every 30 minutes.
Updated 16 variants: rak4631, lilygo_tbeam_SX1262, rak_wismesh_tag,
lilygo_tbeam_supreme_SX1262, thinknode_m3, heltec_v4, thinknode_m1,
lilygo_tbeam_SX1276, meshadventurer, nano_g2_ultra, heltec_v3,
promicro, xiao_c3, heltec_tracker_v2, keepteen_lt1, heltec_mesh_solar.
