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

BoundaryConfig.h

@@ -557,6 +557,10 @@ void config_portal_start() {
         display.display();
     }
     #endif
+    // Headless: LED ramp will be driven from the WCC portal loop
+    if (headless_mode) {
+        Serial.println("[Config] Headless mode — LED will breathe during config portal");
+    }
 }
 
 // ─── Stop Config Portal ──────────────────────────────────────────────────────