Implement GPU-accelerated inpainting using Metal compute shaders:
- Add Shaders.metal with dilateMask, gaussianBlur, diffuseInpaint, edgeAwareBlend kernels
- Add PatchMatchInpainter class for exemplar-based inpainting
- Update InpaintEngine to use Metal with Accelerate fallback
- Add BrushCanvasView for manual brush-based mask painting
- Add LineBrushView for wire removal line drawing
- Update CanvasView to integrate brush canvas overlay
Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>