feat: add album scope for similar image search

Similar search scoping:
- Add current_album as a similar-scope option and remember the source album when similar or region searches are launched from an album.
- Route gallery and lightbox similar actions through scope-aware store helpers so Album/Folder/All choices are applied consistently.
- Keep pagination and scope toggles working for both whole-image and region-search result sets.

Backend filtering:
- Extend find_similar_images and find_similar_by_region params with album_id, giving album scope precedence over folder scope.
- Add album_membership filtering for HNSW whole-image search and brute-force crop embedding search.

src/components/Lightbox.tsx

@@ -144,9 +144,8 @@ export function Lightbox() {
   const closeImage = useGalleryStore((state) => state.closeImage);
   const images = useGalleryStore((state) => state.images);
   const openImage = useGalleryStore((state) => state.openImage);
-  const loadSimilarImages = useGalleryStore((state) => state.loadSimilarImages);
-  const loadSimilarByRegion = useGalleryStore((state) => state.loadSimilarByRegion);
-  const similarScope = useGalleryStore((state) => state.similarScope);
+  const findSimilar = useGalleryStore((state) => state.findSimilar);
+  const findSimilarByRegion = useGalleryStore((state) => state.findSimilarByRegion);
   const updateImageDetails = useGalleryStore((state) => state.updateImageDetails);
   const getImageTags = useGalleryStore((state) => state.getImageTags);
   const addUserTag = useGalleryStore((state) => state.addUserTag);
@@ -384,12 +383,10 @@ export function Lightbox() {
       exitRegionMode();
       setRegionSearching(true);
 
-      const folderId =
-        similarScope === "current_folder" ? selectedImage.folder_id : null;
-      void loadSimilarByRegion(selectedImage.id, crop, folderId, selectedImage.folder_id)
+      void findSimilarByRegion(selectedImage.id, crop, selectedImage.folder_id)
         .finally(() => setRegionSearching(false));
     },
-    [isPanning, isDragging, dragRect, selectedImage, similarScope, loadSimilarByRegion, exitRegionMode],
+    [isPanning, isDragging, dragRect, selectedImage, findSimilarByRegion, exitRegionMode],
   );
 
   // Build the CSS rect for the selection overlay (viewport-relative)
@@ -543,7 +540,7 @@ export function Lightbox() {
                       }`}
                       onClick={() => {
                         if (!canFindSimilar) return;
-                        void loadSimilarImages(selectedImage.id, similarScope === "current_folder" ? selectedImage.folder_id : null, true, selectedImage.folder_id);
+                        void findSimilar(selectedImage.id, selectedImage.folder_id);
                       }}
                       disabled={!canFindSimilar}
                     >