Add Adalight serial LED device support with per-type discovery and capability-based UI

Implements the second device provider (Adalight) for Arduino-based serial LED controllers,
validating the LEDDeviceProvider abstraction. Adds serial port auto-discovery, per-type
discovery caching with lazy-load, capability-driven UI (brightness control, manual LED count,
standby), and serial port combobox in both Add Device and General Settings modals.

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

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

@@ -83,7 +83,12 @@ async def create_device(
 
         try:
             result = await provider.validate_device(device_url)
-            led_count = result["led_count"]
+            led_count = result.get("led_count") or device_data.led_count
+            if not led_count or led_count < 1:
+                raise HTTPException(
+                    status_code=422,
+                    detail="LED count is required for this device type.",
+                )
         except httpx.ConnectError:
             raise HTTPException(
                 status_code=422,
@@ -146,18 +151,28 @@ async def discover_devices(
     _auth: AuthRequired,
     store: DeviceStore = Depends(get_device_store),
     timeout: float = 3.0,
+    device_type: str | None = None,
 ):
-    """Scan the local network for LED devices via all registered providers."""
+    """Scan for LED devices. Optionally filter by device_type (e.g. wled, adalight)."""
     import asyncio
     import time
 
     start = time.time()
     capped_timeout = min(timeout, 10.0)
-    # Discover from all providers in parallel
-    providers = get_all_providers()
-    discover_tasks = [p.discover(timeout=capped_timeout) for p in providers.values()]
-    all_results = await asyncio.gather(*discover_tasks)
-    discovered = [d for batch in all_results for d in batch]
+
+    if device_type:
+        # Discover from a single provider
+        try:
+            provider = get_provider(device_type)
+        except ValueError:
+            raise HTTPException(status_code=400, detail=f"Unknown device type: {device_type}")
+        discovered = await provider.discover(timeout=capped_timeout)
+    else:
+        # Discover from all providers in parallel
+        providers = get_all_providers()
+        discover_tasks = [p.discover(timeout=capped_timeout) for p in providers.values()]
+        all_results = await asyncio.gather(*discover_tasks)
+        discovered = [d for batch in all_results for d in batch]
     elapsed_ms = (time.time() - start) * 1000
 
     existing_urls = {d.url.rstrip("/").lower() for d in store.get_all_devices()}
@@ -213,6 +228,7 @@ async def update_device(
             name=update_data.name,
             url=update_data.url,
             enabled=update_data.enabled,
+            led_count=update_data.led_count,
         )
 
         # Sync connection info in processor manager
@@ -220,7 +236,7 @@ async def update_device(
             manager.update_device_info(
                 device_id,
                 device_url=update_data.url,
-                led_count=None,
+                led_count=update_data.led_count,
             )
         except ValueError:
             pass