feat: add LED indicators and headless mode support for V3/V4

- Detect missing OLED at boot, set headless_mode flag
- LED solid: normal operation (radio online)
- LED fast blink: button held >5s (entering WCC config mode)
- LED slow breathe: WiFi Captive Configure portal active
- Allow 1-3s button press in WCC mode to power off
- Next boot after WCC power-off skips config portal (unless unconfigured)
- LED indicators active on both V3 and V4, with or without display
- Clean up LED PWM on deep sleep

Config.h

@@ -145,6 +145,7 @@
 	bool hw_ready      = false;
 	bool radio_error   = false;
 	bool disp_ready    = false;
+	bool headless_mode = false;
 	bool pmu_ready     = false;
 	bool promisc       = false;
 	bool implicit      = false;