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

Input.h

@@ -96,6 +96,9 @@
             display.display();
           }
           #endif
+          headless_led_fast_blink();
+        } else if (display_lock_white) {
+          headless_led_fast_blink();
         }
       }
     }