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/__init__.py

@@ -56,6 +56,12 @@ from .postprocessing import (
     PostprocessingTemplateUpdate,
     PPTemplateTestRequest,
 )
+from .pattern_templates import (
+    PatternTemplateCreate,
+    PatternTemplateListResponse,
+    PatternTemplateResponse,
+    PatternTemplateUpdate,
+)
 from .picture_sources import (
     ImageValidateRequest,
     ImageValidateResponse,
@@ -109,6 +115,10 @@ __all__ = [
     "PostprocessingTemplateResponse",
     "PostprocessingTemplateUpdate",
     "PPTemplateTestRequest",
+    "PatternTemplateCreate",
+    "PatternTemplateListResponse",
+    "PatternTemplateResponse",
+    "PatternTemplateUpdate",
     "ImageValidateRequest",
     "ImageValidateResponse",
     "PictureSourceCreate",