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/core/processor_manager.py

@@ -155,7 +155,7 @@ class ProcessorManager:
     Targets are registered for processing (streaming sources to devices).
     """
 
-    def __init__(self, picture_source_store=None, capture_template_store=None, pp_template_store=None):
+    def __init__(self, picture_source_store=None, capture_template_store=None, pp_template_store=None, pattern_template_store=None):
         """Initialize processor manager."""
         self._devices: Dict[str, DeviceState] = {}
         self._targets: Dict[str, TargetState] = {}
@@ -165,6 +165,7 @@ class ProcessorManager:
         self._picture_source_store = picture_source_store
         self._capture_template_store = capture_template_store
         self._pp_template_store = pp_template_store
+        self._pattern_template_store = pattern_template_store
         self._live_stream_manager = LiveStreamManager(
             picture_source_store, capture_template_store, pp_template_store
         )
@@ -1054,8 +1055,19 @@ class ProcessorManager:
         if not state.picture_source_id:
             raise ValueError(f"KC target {target_id} has no picture source assigned")
 
-        if not state.settings.rectangles:
-            raise ValueError(f"KC target {target_id} has no rectangles defined")
+        if not state.settings.pattern_template_id:
+            raise ValueError(f"KC target {target_id} has no pattern template assigned")
+
+        # Resolve pattern template to get rectangles
+        try:
+            pattern_template = self._pattern_template_store.get_template(state.settings.pattern_template_id)
+        except (ValueError, AttributeError):
+            raise ValueError(f"Pattern template {state.settings.pattern_template_id} not found")
+
+        if not pattern_template.rectangles:
+            raise ValueError(f"Pattern template {state.settings.pattern_template_id} has no rectangles")
+
+        state._resolved_rectangles = pattern_template.rectangles
 
         # Acquire live stream
         try:
@@ -1133,9 +1145,11 @@ class ProcessorManager:
         frame_time = 1.0 / target_fps
         fps_samples: List[float] = []
 
+        rectangles = state._resolved_rectangles
+
         logger.info(
             f"KC processing loop started for target {target_id} "
-            f"(fps={target_fps}, rects={len(settings.rectangles)})"
+            f"(fps={target_fps}, rects={len(rectangles)})"
         )
 
         try:
@@ -1152,7 +1166,7 @@ class ProcessorManager:
                     h, w = img.shape[:2]
 
                     colors: Dict[str, Tuple[int, int, int]] = {}
-                    for rect in settings.rectangles:
+                    for rect in rectangles:
                         # Convert relative coords to pixel coords
                         px_x = max(0, int(rect.x * w))
                         px_y = max(0, int(rect.y * h))