Add WLED auto-discovery via mDNS with zeroconf

Scan the local network for WLED devices advertising _wled._tcp.local.
and present them in the Add Device modal for one-click selection.

- New discovery.py: async mDNS browse + parallel /json/info enrichment
- GET /api/v1/devices/discover endpoint with already_added dedup
- Header scan button (magnifying glass icon) in add-device modal
- Discovered devices show name, IP, LED count, version; click to fill form
- en/ru locale strings for discovery UI

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

server/src/wled_controller/api/routes/devices.py

@@ -19,6 +19,8 @@ from wled_controller.api.schemas.devices import (
     DeviceResponse,
     DeviceStateResponse,
     DeviceUpdate,
+    DiscoveredDeviceResponse,
+    DiscoverDevicesResponse,
 )
 from wled_controller.core.calibration import (
     calibration_from_dict,
@@ -143,6 +145,45 @@ async def list_devices(
     return DeviceListResponse(devices=responses, count=len(responses))
 
 
+@router.get("/api/v1/devices/discover", response_model=DiscoverDevicesResponse, tags=["Devices"])
+async def discover_devices(
+    _auth: AuthRequired,
+    store: DeviceStore = Depends(get_device_store),
+    timeout: float = 3.0,
+):
+    """Scan the local network for WLED devices via mDNS."""
+    import time
+    from wled_controller.core.discovery import discover_wled_devices
+
+    start = time.time()
+    discovered = await discover_wled_devices(timeout=min(timeout, 10.0))
+    elapsed_ms = (time.time() - start) * 1000
+
+    existing_urls = {d.url.rstrip("/").lower() for d in store.get_all_devices()}
+
+    results = []
+    for d in discovered:
+        already_added = d.url.rstrip("/").lower() in existing_urls
+        results.append(
+            DiscoveredDeviceResponse(
+                name=d.name,
+                url=d.url,
+                device_type=d.device_type,
+                ip=d.ip,
+                mac=d.mac,
+                led_count=d.led_count,
+                version=d.version,
+                already_added=already_added,
+            )
+        )
+
+    return DiscoverDevicesResponse(
+        devices=results,
+        count=len(results),
+        scan_duration_ms=round(elapsed_ms, 1),
+    )
+
+
 @router.get("/api/v1/devices/{device_id}", response_model=DeviceResponse, tags=["Devices"])
 async def get_device(
     device_id: str,