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/routes/picture_targets.py

@@ -12,7 +12,6 @@ from wled_controller.api.dependencies import (
 )
 from wled_controller.api.schemas.picture_targets import (
     ExtractedColorResponse,
-    KeyColorRectangleSchema,
     KeyColorsResponse,
     KeyColorsSettingsSchema,
     PictureTargetCreate,
@@ -28,7 +27,6 @@ from wled_controller.core.processor_manager import ProcessorManager, ProcessingS
 from wled_controller.storage import DeviceStore
 from wled_controller.storage.wled_picture_target import WledPictureTarget
 from wled_controller.storage.key_colors_picture_target import (
-    KeyColorRectangle,
     KeyColorsSettings,
     KeyColorsPictureTarget,
 )
@@ -84,10 +82,7 @@ def _kc_settings_to_schema(settings: KeyColorsSettings) -> KeyColorsSettingsSche
         fps=settings.fps,
         interpolation_mode=settings.interpolation_mode,
         smoothing=settings.smoothing,
-        rectangles=[
-            KeyColorRectangleSchema(name=r.name, x=r.x, y=r.y, width=r.width, height=r.height)
-            for r in settings.rectangles
-        ],
+        pattern_template_id=settings.pattern_template_id,
     )
 
 
@@ -97,10 +92,7 @@ def _kc_schema_to_settings(schema: KeyColorsSettingsSchema) -> KeyColorsSettings
         fps=schema.fps,
         interpolation_mode=schema.interpolation_mode,
         smoothing=schema.smoothing,
-        rectangles=[
-            KeyColorRectangle(name=r.name, x=r.x, y=r.y, width=r.width, height=r.height)
-            for r in schema.rectangles
-        ],
+        pattern_template_id=schema.pattern_template_id,
     )