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/scripts/start-server.bat

@@ -0,0 +1,15 @@
+@echo off
+REM WLED Screen Controller Startup Script
+REM This script starts the WLED screen controller server
+
+echo Starting WLED Screen Controller...
+echo.
+
+REM Change to the server directory (parent of scripts folder)
+cd /d "%~dp0\.."
+
+REM Start the server
+python -m uvicorn wled_controller.main:app --host 0.0.0.0 --port 8080
+
+REM If the server exits, pause to show any error messages
+pause