Refactor capture engine architecture, rename PictureStream to PictureSource, and split API modules

- Separate CaptureEngine into stateless factory + stateful CaptureStream session
- Add LiveStream/LiveStreamManager for shared capture with reference counting
- Rename PictureStream to PictureSource across storage, API, and UI
- Remove legacy migration logic and unused compatibility code
- Split monolithic routes.py (1935 lines) into 5 focused route modules
- Split schemas.py (480 lines) into 7 schema modules with re-exports
- Extract dependency injection into dedicated dependencies.py

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

server/src/wled_controller/storage/postprocessing_template.py

@@ -31,25 +31,8 @@ class PostprocessingTemplate:
 
     @classmethod
     def from_dict(cls, data: dict) -> "PostprocessingTemplate":
-        """Create template from dictionary.
-
-        Supports migration from legacy flat-field format (gamma/saturation/brightness)
-        to the new filters list format.
-        """
-        if "filters" in data:
-            filters = [FilterInstance.from_dict(f) for f in data["filters"]]
-        else:
-            # Legacy migration: construct filters from flat fields
-            filters = []
-            brightness = data.get("brightness", 1.0)
-            if brightness != 1.0:
-                filters.append(FilterInstance("brightness", {"value": brightness}))
-            saturation = data.get("saturation", 1.0)
-            if saturation != 1.0:
-                filters.append(FilterInstance("saturation", {"value": saturation}))
-            gamma = data.get("gamma", 2.2)
-            if gamma != 2.2:
-                filters.append(FilterInstance("gamma", {"value": gamma}))
+        """Create template from dictionary."""
+        filters = [FilterInstance.from_dict(f) for f in data.get("filters", [])]
 
         return cls(
             id=data["id"],