Remove idle color feature, simplify power to turn-off only, fix settings serial port bug

- Remove static/idle color from entire stack (storage, API, processing, UI, CSS, locales)
- Simplify device power button to turn-off only (send black frame, no toggle)
- Send black frame on serial port close (AdalightClient.close)
- Fix settings modal serial port dropdown showing WLED devices due to stale deviceType

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

server/src/wled_controller/static/locales/en.json

@@ -131,8 +131,7 @@
   "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.button.power_off": "Turn Off",
   "device.power.off_success": "Device turned off",
   "device.status.connected": "Connected",
   "device.status.disconnected": "Disconnected",
@@ -159,9 +158,6 @@
   "device.health.online": "Online",
   "device.health.offline": "Offline",
   "device.health.checking": "Checking...",
-  "device.static_color": "Idle Color",
-  "device.static_color.hint": "Color shown when device is idle",
-  "device.static_color.clear": "Clear idle color",
   "device.tutorial.start": "Start tutorial",
   "device.tip.metadata": "Device info (LED count, type, color channels) is auto-detected from the device",
   "device.tip.brightness": "Slide to adjust device brightness",