Add Key Colors target type for extracting colors from screen regions

Introduce a new "key_colors" target type alongside WLED targets, enabling
real-time color extraction from configurable screen rectangles with
average/median/dominant modes, temporal smoothing, and WebSocket streaming.

- Split WledPictureTarget into its own module, add KeyColorsPictureTarget
- Add KC target lifecycle to ProcessorManager (register, start/stop, processing loop)
- Extend API routes and schemas for KC targets (CRUD, settings, state, metrics, colors)
- Add WebSocket endpoint for real-time color updates with auth
- Add KC sub-tab in Targets UI with editor modal and live color swatches
- Add EN and RU translations for all key colors strings

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

server/src/wled_controller/storage/wled_picture_target.py

@@ -0,0 +1,65 @@
+"""WLED picture target — streams a picture source to a WLED device."""
+
+from dataclasses import dataclass, field
+from datetime import datetime
+from typing import Optional
+
+from wled_controller.core.processor_manager import ProcessingSettings
+from wled_controller.storage.picture_target import PictureTarget
+
+
+@dataclass
+class WledPictureTarget(PictureTarget):
+    """WLED picture target — streams a picture source to a WLED device."""
+
+    device_id: str = ""
+    picture_source_id: str = ""
+    settings: ProcessingSettings = field(default_factory=ProcessingSettings)
+
+    def to_dict(self) -> dict:
+        """Convert to dictionary."""
+        d = super().to_dict()
+        d["device_id"] = self.device_id
+        d["picture_source_id"] = self.picture_source_id
+        d["settings"] = {
+            "display_index": self.settings.display_index,
+            "fps": self.settings.fps,
+            "border_width": self.settings.border_width,
+            "brightness": self.settings.brightness,
+            "gamma": self.settings.gamma,
+            "saturation": self.settings.saturation,
+            "smoothing": self.settings.smoothing,
+            "interpolation_mode": self.settings.interpolation_mode,
+            "state_check_interval": self.settings.state_check_interval,
+        }
+        return d
+
+    @classmethod
+    def from_dict(cls, data: dict) -> "WledPictureTarget":
+        """Create from dictionary."""
+        from wled_controller.core.processor_manager import DEFAULT_STATE_CHECK_INTERVAL
+
+        settings_data = data.get("settings", {})
+        settings = ProcessingSettings(
+            display_index=settings_data.get("display_index", 0),
+            fps=settings_data.get("fps", 30),
+            border_width=settings_data.get("border_width", 10),
+            brightness=settings_data.get("brightness", 1.0),
+            gamma=settings_data.get("gamma", 2.2),
+            saturation=settings_data.get("saturation", 1.0),
+            smoothing=settings_data.get("smoothing", 0.3),
+            interpolation_mode=settings_data.get("interpolation_mode", "average"),
+            state_check_interval=settings_data.get("state_check_interval", DEFAULT_STATE_CHECK_INTERVAL),
+        )
+
+        return cls(
+            id=data["id"],
+            name=data["name"],
+            target_type=data.get("target_type", "wled"),
+            device_id=data.get("device_id", ""),
+            picture_source_id=data.get("picture_source_id", ""),
+            settings=settings,
+            description=data.get("description"),
+            created_at=datetime.fromisoformat(data.get("created_at", datetime.utcnow().isoformat())),
+            updated_at=datetime.fromisoformat(data.get("updated_at", datetime.utcnow().isoformat())),
+        )