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/system.py

@@ -0,0 +1,42 @@
+"""System-related schemas (health, version, displays)."""
+
+from datetime import datetime
+from typing import List, Literal
+
+from pydantic import BaseModel, Field
+
+
+class HealthResponse(BaseModel):
+    """Health check response."""
+
+    status: Literal["healthy", "unhealthy"] = Field(description="Service health status")
+    timestamp: datetime = Field(description="Current server time")
+    version: str = Field(description="Application version")
+
+
+class VersionResponse(BaseModel):
+    """Version information response."""
+
+    version: str = Field(description="Application version")
+    python_version: str = Field(description="Python version")
+    api_version: str = Field(description="API version")
+
+
+class DisplayInfo(BaseModel):
+    """Display/monitor information."""
+
+    index: int = Field(description="Display index")
+    name: str = Field(description="Display name")
+    width: int = Field(description="Display width in pixels")
+    height: int = Field(description="Display height in pixels")
+    x: int = Field(description="Display X position")
+    y: int = Field(description="Display Y position")
+    is_primary: bool = Field(default=False, description="Whether this is the primary display")
+    refresh_rate: int = Field(description="Display refresh rate in Hz")
+
+
+class DisplayListResponse(BaseModel):
+    """List of available displays."""
+
+    displays: List[DisplayInfo] = Field(description="Available displays")
+    count: int = Field(description="Number of displays")