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/core/calibration.py

@@ -32,6 +32,7 @@ class CalibrationConfig:
     layout: Literal["clockwise", "counterclockwise"]
     start_position: Literal["top_left", "top_right", "bottom_left", "bottom_right"]
     segments: List[CalibrationSegment]
+    offset: int = 0  # Physical LED offset from start corner (number of LEDs from LED 0 to start corner)
 
     def validate(self) -> bool:
         """Validate calibration configuration.
@@ -181,7 +182,14 @@ class PixelMapper:
                 color = self._calc_color(pixel_segment)
                 led_colors[led_idx] = color
 
-        logger.debug(f"Mapped border pixels to {total_leds} LED colors")
+        # Apply physical LED offset by rotating the array
+        # Offset = number of LEDs from LED 0 to the start corner
+        # Physical LED[i] should get calibration color[(i - offset) % total]
+        offset = self.calibration.offset % total_leds if total_leds > 0 else 0
+        if offset > 0:
+            led_colors = led_colors[total_leds - offset:] + led_colors[:total_leds - offset]
+
+        logger.debug(f"Mapped border pixels to {total_leds} LED colors (offset={offset})")
         return led_colors
 
     def test_calibration(self, edge: str, color: Tuple[int, int, int]) -> List[Tuple[int, int, int]]:
@@ -309,6 +317,7 @@ def calibration_from_dict(data: dict) -> CalibrationConfig:
             layout=data["layout"],
             start_position=data["start_position"],
             segments=segments,
+            offset=data.get("offset", 0),
         )
 
         config.validate()
@@ -332,6 +341,7 @@ def calibration_to_dict(config: CalibrationConfig) -> dict:
     return {
         "layout": config.layout,
         "start_position": config.start_position,
+        "offset": config.offset,
         "segments": [
             {
                 "edge": seg.edge,