Add WLED health monitoring, calibration test mode, and UI improvements

- Add background health checks (GET /json/info) with configurable interval per device
- Auto-detect LED count from WLED device on add (remove led_count from create API)
- Add calibration test mode: toggle edges on/off with colored LEDs via PUT endpoint
- Show WLED firmware version badge and LED count badge on device cards
- Add modal dirty tracking with discard confirmation on close/backdrop click
- Fix layout jump when modals open by compensating for scrollbar width
- Add state_check_interval to settings API and UI

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

server/src/wled_controller/storage/device_store.py

@@ -12,7 +12,7 @@ from wled_controller.core.calibration import (
     calibration_to_dict,
     create_default_calibration,
 )
-from wled_controller.core.processor_manager import ProcessingSettings
+from wled_controller.core.processor_manager import DEFAULT_STATE_CHECK_INTERVAL, ProcessingSettings
 from wled_controller.utils import get_logger
 
 logger = get_logger(__name__)
@@ -77,6 +77,7 @@ class Device:
                 "saturation": self.settings.saturation,
                 "smoothing": self.settings.smoothing,
                 "interpolation_mode": self.settings.interpolation_mode,
+                "state_check_interval": self.settings.state_check_interval,
             },
             "calibration": calibration_to_dict(self.calibration),
             "created_at": self.created_at.isoformat(),
@@ -103,6 +104,10 @@ class Device:
             saturation=settings_data.get("saturation", 1.0),
             smoothing=settings_data.get("smoothing", 0.3),
             interpolation_mode=settings_data.get("interpolation_mode", "average"),
+            state_check_interval=settings_data.get(
+                "state_check_interval",
+                settings_data.get("health_check_interval", DEFAULT_STATE_CHECK_INTERVAL),
+            ),
         )
 
         calibration_data = data.get("calibration")