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/static/locales/en.json

@@ -130,6 +130,9 @@
   "device.button.calibrate": "Calibrate",
   "device.button.remove": "Remove",
   "device.button.webui": "Open Device Web UI",
+  "device.button.power_toggle": "Toggle Power",
+  "device.power.on_success": "Device turned on",
+  "device.power.off_success": "Device turned off",
   "device.status.connected": "Connected",
   "device.status.disconnected": "Disconnected",
   "device.status.error": "Error",