Add Pattern Templates for Key Colors targets with visual canvas editor

Introduce Pattern Template entity as a reusable rectangle layout that
Key Colors targets reference via pattern_template_id. This replaces
inline rectangle storage with a shared template system.

Backend:
- New PatternTemplate data model, store (JSON persistence), CRUD API
- KC targets now reference pattern_template_id instead of inline rectangles
- ProcessorManager resolves pattern template at KC processing start
- Picture source test endpoint supports capture_duration=0 for single frame
- Delete protection: 409 when template is referenced by a KC target

Frontend:
- Pattern Templates section in Key Colors sub-tab with card UI
- Visual canvas editor with drag-to-move, 8-point resize handles
- Background capture from any picture source for visual alignment
- Precise coordinate list synced bidirectionally with canvas
- Resizable editor container, viewport-constrained modal
- KC target editor uses pattern template dropdown instead of inline rects
- Localization (en/ru) for all new UI elements

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

server/src/wled_controller/api/schemas/picture_targets.py

@@ -51,7 +51,7 @@ class KeyColorsSettingsSchema(BaseModel):
     fps: int = Field(default=10, description="Extraction rate (1-60)", ge=1, le=60)
     interpolation_mode: str = Field(default="average", description="Color mode (average, median, dominant)")
     smoothing: float = Field(default=0.3, description="Temporal smoothing (0.0-1.0)", ge=0.0, le=1.0)
-    rectangles: List[KeyColorRectangleSchema] = Field(default_factory=list, description="Rectangles to extract colors from")
+    pattern_template_id: str = Field(default="", description="Pattern template ID for rectangle layout")
 
 
 class ExtractedColorResponse(BaseModel):