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/__init__.py

@@ -7,6 +7,7 @@ from .routes.devices import router as devices_router
 from .routes.templates import router as templates_router
 from .routes.postprocessing import router as postprocessing_router
 from .routes.picture_sources import router as picture_sources_router
+from .routes.pattern_templates import router as pattern_templates_router
 from .routes.picture_targets import router as picture_targets_router
 
 router = APIRouter()
@@ -14,6 +15,7 @@ router.include_router(system_router)
 router.include_router(devices_router)
 router.include_router(templates_router)
 router.include_router(postprocessing_router)
+router.include_router(pattern_templates_router)
 router.include_router(picture_sources_router)
 router.include_router(picture_targets_router)