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/main.py

@@ -17,6 +17,7 @@ from wled_controller.core.processor_manager import ProcessorManager, ProcessingS
 from wled_controller.storage import DeviceStore
 from wled_controller.storage.template_store import TemplateStore
 from wled_controller.storage.postprocessing_template_store import PostprocessingTemplateStore
+from wled_controller.storage.pattern_template_store import PatternTemplateStore
 from wled_controller.storage.picture_source_store import PictureSourceStore
 from wled_controller.storage.picture_target_store import PictureTargetStore
 from wled_controller.storage.wled_picture_target import WledPictureTarget
@@ -36,11 +37,13 @@ template_store = TemplateStore(config.storage.templates_file)
 pp_template_store = PostprocessingTemplateStore(config.storage.postprocessing_templates_file)
 picture_source_store = PictureSourceStore(config.storage.picture_sources_file)
 picture_target_store = PictureTargetStore(config.storage.picture_targets_file)
+pattern_template_store = PatternTemplateStore(config.storage.pattern_templates_file)
 
 processor_manager = ProcessorManager(
     picture_source_store=picture_source_store,
     capture_template_store=template_store,
     pp_template_store=pp_template_store,
+    pattern_template_store=pattern_template_store,
 )
 
 
@@ -130,13 +133,14 @@ async def lifespan(app: FastAPI):
     logger.info(f"Authorized clients: {client_labels}")
     logger.info("All API requests require valid Bearer token authentication")
 
-    # Run migration from legacy device settings to picture targets
+    # Run migrations
     _migrate_devices_to_targets()
 
     # Initialize API dependencies
     init_dependencies(
         device_store, template_store, processor_manager,
         pp_template_store=pp_template_store,
+        pattern_template_store=pattern_template_store,
         picture_source_store=picture_source_store,
         picture_target_store=picture_target_store,
     )