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/api/schemas/postprocessing.py

@@ -0,0 +1,49 @@
+"""Postprocessing template schemas."""
+
+from datetime import datetime
+from typing import List, Optional
+
+from pydantic import BaseModel, Field
+
+from .filters import FilterInstanceSchema
+
+
+class PostprocessingTemplateCreate(BaseModel):
+    """Request to create a postprocessing template."""
+
+    name: str = Field(description="Template name", min_length=1, max_length=100)
+    filters: List[FilterInstanceSchema] = Field(default_factory=list, description="Ordered list of filter instances")
+    description: Optional[str] = Field(None, description="Template description", max_length=500)
+
+
+class PostprocessingTemplateUpdate(BaseModel):
+    """Request to update a postprocessing template."""
+
+    name: Optional[str] = Field(None, description="Template name", min_length=1, max_length=100)
+    filters: Optional[List[FilterInstanceSchema]] = Field(None, description="Ordered list of filter instances")
+    description: Optional[str] = Field(None, description="Template description", max_length=500)
+
+
+class PostprocessingTemplateResponse(BaseModel):
+    """Postprocessing template information response."""
+
+    id: str = Field(description="Template ID")
+    name: str = Field(description="Template name")
+    filters: List[FilterInstanceSchema] = Field(description="Ordered list of filter instances")
+    created_at: datetime = Field(description="Creation timestamp")
+    updated_at: datetime = Field(description="Last update timestamp")
+    description: Optional[str] = Field(None, description="Template description")
+
+
+class PostprocessingTemplateListResponse(BaseModel):
+    """List of postprocessing templates response."""
+
+    templates: List[PostprocessingTemplateResponse] = Field(description="List of postprocessing templates")
+    count: int = Field(description="Number of templates")
+
+
+class PPTemplateTestRequest(BaseModel):
+    """Request to test a postprocessing template against a source stream."""
+
+    source_stream_id: str = Field(description="ID of the source picture source to capture from")
+    capture_duration: float = Field(default=5.0, ge=1.0, le=30.0, description="Duration to capture in seconds")