Add power toggle button to LED device cards

WLED: native on/off via JSON API. Adalight: sends all-black frame
to blank LEDs (uses existing client if target is running, otherwise
opens temporary serial connection). Toggle button placed next to
delete button in card top-right corner.

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

server/src/wled_controller/core/adalight_provider.py

@@ -24,7 +24,8 @@ class AdalightDeviceProvider(LEDDeviceProvider):
     def capabilities(self) -> set:
         # No hardware brightness control, no standby required
         # manual_led_count: user must specify LED count (can't auto-detect)
-        return {"manual_led_count"}
+        # power_control: can blank LEDs by sending all-black pixels
+        return {"manual_led_count", "power_control"}
 
     def create_client(self, url: str, **kwargs) -> LEDClient:
         from wled_controller.core.adalight_client import AdalightClient
@@ -92,3 +93,12 @@ class AdalightDeviceProvider(LEDDeviceProvider):
         except Exception as e:
             logger.error(f"Serial port discovery failed: {e}")
             return []
+
+    async def get_power(self, url: str) -> bool:
+        # Adalight has no hardware power query; assume on
+        return True
+
+    async def set_power(self, url: str, on: bool) -> None:
+        # Adalight power control is handled at the API layer via processor manager
+        # because it needs access to the active serial client or device info.
+        raise NotImplementedError("Use API-level set_power for Adalight")

server/src/wled_controller/core/led_client.py

@@ -200,6 +200,14 @@ class LEDDeviceProvider(ABC):
         """Set device brightness (0-255). Override if capabilities include brightness_control."""
         raise NotImplementedError
 
+    async def get_power(self, url: str) -> bool:
+        """Get device power state. Override if capabilities include power_control."""
+        raise NotImplementedError
+
+    async def set_power(self, url: str, on: bool) -> None:
+        """Set device power state. Override if capabilities include power_control."""
+        raise NotImplementedError
+
 
 # ===== PROVIDER REGISTRY =====
 

server/src/wled_controller/core/processor_manager.py

@@ -382,6 +382,35 @@ class ProcessorManager:
 
         logger.info(f"Updated calibration for device {device_id}")
 
+    async def send_black_frame(self, device_id: str) -> None:
+        """Send an all-black frame to an Adalight device to blank its LEDs.
+
+        Uses the existing client from a running target if available,
+        otherwise opens a temporary serial connection.
+        """
+        if device_id not in self._devices:
+            raise ValueError(f"Device {device_id} not found")
+
+        ds = self._devices[device_id]
+        black = np.zeros((ds.led_count, 3), dtype=np.uint8)
+
+        # Try to use existing client from a running target
+        for ts in self._targets.values():
+            if ts.device_id == device_id and ts.is_running and ts.led_client:
+                await ts.led_client.send_pixels(black, brightness=255)
+                return
+
+        # No running target — open a temporary connection
+        client = create_led_client(
+            ds.device_type, ds.device_url,
+            led_count=ds.led_count, baud_rate=ds.baud_rate,
+        )
+        try:
+            await client.connect()
+            await client.send_pixels(black, brightness=255)
+        finally:
+            await client.close()
+
     def get_device_state(self, device_id: str) -> DeviceState:
         """Get device state (for health/calibration info)."""
         if device_id not in self._devices:

server/src/wled_controller/core/wled_provider.py

@@ -30,7 +30,7 @@ class WLEDDeviceProvider(LEDDeviceProvider):
 
     @property
     def capabilities(self) -> set:
-        return {"brightness_control", "standby_required"}
+        return {"brightness_control", "power_control", "standby_required"}
 
     def create_client(self, url: str, **kwargs) -> LEDClient:
         from wled_controller.core.wled_client import WLEDClient
@@ -170,3 +170,19 @@ class WLEDDeviceProvider(LEDDeviceProvider):
                 json={"bri": brightness},
             )
             resp.raise_for_status()
+
+    async def get_power(self, url: str) -> bool:
+        url = url.rstrip("/")
+        async with httpx.AsyncClient(timeout=5.0) as http_client:
+            resp = await http_client.get(f"{url}/json/state")
+            resp.raise_for_status()
+            return resp.json().get("on", False)
+
+    async def set_power(self, url: str, on: bool) -> None:
+        url = url.rstrip("/")
+        async with httpx.AsyncClient(timeout=5.0) as http_client:
+            resp = await http_client.post(
+                f"{url}/json/state",
+                json={"on": on},
+            )
+            resp.raise_for_status()