feat: add manual crop mode

- CropOverlay component with draggable/resizable region
- Maintains target device aspect ratio
- Rule of thirds grid overlay
- Dark mask outside crop area
- Updates ImagePreview to show overlay in manual mode
- Updates photonWorker to handle manual crop regions
- Also fixes top/bottom crop modes

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

src/lib/components/PipelinePanel.svelte

@@ -47,7 +47,7 @@
 		{ value: 'center', label: 'Center' },
 		{ value: 'top', label: 'Top' },
 		{ value: 'bottom', label: 'Bottom' },
-		{ value: 'manual', label: 'Manual (coming soon)' }
+		{ value: 'manual', label: 'Manual' }
 	];
 
 	const resizeModes: { value: ResizeMode; label: string }[] = [