fix: complete image pipeline - rotation, URL, preview

- Add rotation_degrees parameter to ImageProcessor.process_photo()
- Pass rotation through _auto_save_photo_from_extraction() to processor
- Allow no-crop fallback when crop_bounds is None
- Add buildPhotoUrl() helper to resolve backend URLs correctly
- Update frontend components to use backend URL for image sources
- Replace Use/Skip Photo buttons with checkbox in AI extraction UI
- Add images/ to .gitignore to prevent accidental commits

Addresses: rotation never applied, image 404s (relative to Next.js not backend), preview blank in edit form

frontend/components/AIOnboarding.tsx

@@ -237,23 +237,15 @@ export default function AIOnboarding({ onCancel, onComplete, categories, invento
               </div>
               <div className="p-3 space-y-2">
                 <p className="text-xs text-muted font-normal">Extracted Photo</p>
-                <div className="flex gap-2">
-                  <button
-                    onClick={() => updateEditingItem({ _skipPhoto: false })}
-                    className="flex-1 px-3 py-2 bg-green-500/20 border border-green-500/50 text-green-400 rounded-lg hover:bg-green-500/30 transition-colors font-normal text-xs"
-                  >
-                    Use Photo
-                  </button>
-                  <button
-                    onClick={() => updateEditingItem({ _skipPhoto: true })}
-                    className="flex-1 px-3 py-2 bg-rose-500/20 border border-rose-500/50 text-rose-400 rounded-lg hover:bg-rose-500/30 transition-colors font-normal text-xs"
-                  >
-                    Skip Photo
-                  </button>
-                </div>
-                {extractedItems[editingIndex]._skipPhoto && (
-                  <p className="text-xs text-rose-400/80">Photo will not be saved</p>
-                )}
+                <label className="flex items-center gap-2 cursor-pointer">
+                  <input
+                    type="checkbox"
+                    checked={!extractedItems[editingIndex]._skipPhoto}
+                    onChange={(e) => updateEditingItem({ _skipPhoto: !e.target.checked })}
+                    className="w-4 h-4 accent-primary cursor-pointer"
+                  />
+                  <span className="text-xs text-secondary font-normal">Save this photo with the item</span>
+                </label>
               </div>
             </div>
           )}