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/config/default_config.yaml

@@ -10,10 +10,7 @@ auth:
   # Format: label: "api-key"
   api_keys:
     # Generate secure keys: openssl rand -hex 32
-    # IMPORTANT: Add at least one key before starting the server
-    # home_assistant: "your-secure-api-key-1"
-    # web_dashboard: "your-secure-api-key-2"
-    # monitoring_script: "your-secure-api-key-3"
+    dev: "development-key-change-in-production"  # Development key - CHANGE THIS!
 
 processing:
   default_fps: 30