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/api/schemas.py

@@ -106,6 +106,11 @@ class Calibration(BaseModel):
         default="bottom_left",
         description="Position of LED index 0"
     )
+    offset: int = Field(
+        default=0,
+        ge=0,
+        description="Number of LEDs from physical LED 0 to start corner (along strip direction)"
+    )
     segments: List[CalibrationSegment] = Field(
         description="LED segments for each screen edge",
         min_length=1,