feat: Add inpainting (局部重绘) feature for timeline editor

- Add canvas-based mask drawing tools (brush, eraser, rect, lasso)
- Add undo/redo history support for mask editing
- Integrate inpainting UI into preview player
- Add backend API endpoint for inpainting requests
- Add MediaService.inpaint method with ComfyUI workflow support
- Add Flux inpainting workflows for selfhost and RunningHub

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

api/schemas/editor.py

@@ -108,3 +108,16 @@ class RegenerateAudioResponse(BaseModel):
     duration: float
     success: bool = True
 
+
+class InpaintRequest(BaseModel):
+    """Request to inpaint (局部重绘) frame image"""
+    mask: str = Field(..., description="Base64 encoded mask image (white=inpaint, black=keep)")
+    prompt: Optional[str] = Field(None, description="Optional prompt for inpainted region")
+    denoise_strength: float = Field(0.8, ge=0.0, le=1.0, description="Denoise strength (0.0-1.0)")
+
+
+class InpaintResponse(BaseModel):
+    """Response after inpainting"""
+    image_path: str
+    success: bool = True
+