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/stop-server.bat

@@ -0,0 +1,19 @@
+@echo off
+REM WLED Screen Controller Stop Script
+REM This script stops the running WLED screen controller server
+
+echo Stopping WLED Screen Controller...
+echo.
+
+REM Find and kill Python processes running wled_controller.main
+for /f "tokens=2" %%i in ('tasklist /FI "IMAGENAME eq python.exe" /FO LIST ^| findstr /B "PID:"') do (
+    wmic process where "ProcessId=%%i" get CommandLine 2>nul | findstr /C:"wled_controller.main" >nul
+    if not errorlevel 1 (
+        taskkill /PID %%i /F
+        echo WLED controller process (PID %%i) terminated.
+    )
+)
+
+echo.
+echo Done! WLED Screen Controller stopped.
+pause