Add DDP protocol support, fix event loop blocking, and add LED offset calibration

- Add DDP client for LED strips >500 LEDs (UDP port 4048), with automatic
  fallback from HTTP JSON API when LED count exceeds limit
- Wrap blocking operations (screen capture, image processing) in
  asyncio.to_thread() to prevent event loop starvation
- Turn on WLED device and enable live mode when starting DDP streaming
- Add LED strip offset field to calibration (rotates color array to match
  physical LED position vs start corner)
- Add server management scripts (start, stop, restart, background start)
- Fix WebUI auth error handling and auto-refresh loop
- Add development API key to default config
- Add i18n translations for offset field (en/ru)

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

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

@@ -93,6 +93,8 @@
   "calibration.direction": "Direction:",
   "calibration.direction.clockwise": "Clockwise",
   "calibration.direction.counterclockwise": "Counterclockwise",
+  "calibration.offset": "LED Offset:",
+  "calibration.offset_hint": "LEDs from LED 0 to start corner (along strip)",
   "calibration.leds.top": "Top LEDs:",
   "calibration.leds.right": "Right LEDs:",
   "calibration.leds.bottom": "Bottom LEDs:",