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/pattern_templates.py

@@ -0,0 +1,42 @@
+"""Pydantic schemas for pattern template API."""
+
+from datetime import datetime
+from typing import List, Optional
+
+from pydantic import BaseModel, Field
+
+from .picture_targets import KeyColorRectangleSchema
+
+
+class PatternTemplateCreate(BaseModel):
+    """Request to create a pattern template."""
+
+    name: str = Field(description="Template name", min_length=1, max_length=100)
+    rectangles: List[KeyColorRectangleSchema] = Field(default_factory=list, description="List of named rectangles")
+    description: Optional[str] = Field(None, description="Template description", max_length=500)
+
+
+class PatternTemplateUpdate(BaseModel):
+    """Request to update a pattern template."""
+
+    name: Optional[str] = Field(None, description="Template name", min_length=1, max_length=100)
+    rectangles: Optional[List[KeyColorRectangleSchema]] = Field(None, description="List of named rectangles")
+    description: Optional[str] = Field(None, description="Template description", max_length=500)
+
+
+class PatternTemplateResponse(BaseModel):
+    """Pattern template response."""
+
+    id: str = Field(description="Template ID")
+    name: str = Field(description="Template name")
+    rectangles: List[KeyColorRectangleSchema] = Field(description="List of named rectangles")
+    created_at: datetime = Field(description="Creation timestamp")
+    updated_at: datetime = Field(description="Last update timestamp")
+    description: Optional[str] = Field(None, description="Template description")
+
+
+class PatternTemplateListResponse(BaseModel):
+    """List of pattern templates."""
+
+    templates: List[PatternTemplateResponse] = Field(description="List of pattern templates")
+    count: int = Field(description="Number of templates")