feat: hide-from-views flag on folders

Adds a per-folder "hide from views" toggle so noisy subtrees
(screenshots, WhatsApp dumps, work archives) can be excluded from
cross-cutting views without losing indexing. Photos under a hidden
folder are still scanned, thumbnailed, embedded, OCR'd, face-
extracted — they just stop appearing in All Photos, Rated, Colors,
Map, Tags, People, Search, Duplicates, and the sidebar counts.
Navigating directly into the folder still shows every photo.

Schema (migration 0007_folder_hidden):
- folders.is_hidden   user-set toggle, default false
- photos.is_hidden    denormalized effective flag (true iff any
                      ancestor folder is hidden), indexed so cross-
                      cutting queries stay on the existing planner
                      paths

The denorm is maintained by two paths:
- The scanner walks the ancestry chain on insert, with a per-scan
  memoized cache so each folder is resolved once per scan.
- POST /api/v1/folders/{id}/hide flips folders.is_hidden and runs a
  WITH RECURSIVE CTE to recompute every folder's effective state in
  one query, then bulk-updates photos WHERE IS DISTINCT FROM. Runs
  in ~10 ms on a 13k-photo library.

Filters added (cross-cutting queries):
- /library/stats — every sidebar badge via a shared `visible` filter
- /photos (list) — only when neither folder_id nor heap_id is set;
  folder browse and heap browse always show everything
- /photos/map
- /library/duplicates/groups
- /folders/tree photo_count subquery
- /tags count_subq (drives Tags + People sidebar counts)
- services/duplicates.regroup_duplicates (so hidden dupes never
  contaminate the Duplicates view)
- services/search.hybrid_search — both semantic (pgvector) and FTS
  legs join photos so rankings don't include hidden results

Intentionally NOT filtered:
- /photos?folder_id=X and /photos?heap_id=X (user-intentional browse)
- /library/maintenance/pipeline-stats (tracks real worker state)
- cleanup service (disk-level ops, not views)

Frontend:
- sourceFolders.setHidden(id, hidden) API client method
- FolderTreeNode.is_hidden carried through the tree into TreeItem
- LeftSidebar kebab menu: "Hide from views" / "Show in views" with a
  mutation that invalidates folders, photos, stats, and tags caches
- Hidden folder rows swap the Folder icon for EyeOff and render the
  label italic/muted so the state is visible at a glance

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

frontend/src/services/api.ts

@@ -22,6 +22,11 @@ export interface FolderTreeNode {
   name: string
   path: string
   photo_count: number
+  /** User-set "hide from cross-cutting views" flag. When true, photos
+   *  in this folder (and descendants) are excluded from All Photos,
+   *  Map, Tags, People, Search and sidebar counts, but remain visible
+   *  when the user navigates directly into the folder. */
+  is_hidden: boolean
   children: FolderTreeNode[]
 }
 
@@ -60,6 +65,23 @@ export const sourceFolders = {
     return response.data as { id: string; name: string; path: string; parent_id: string }
   },
 
+  /** Toggle "hide from views" on a folder or source root. Hidden
+   *  folders still index + thumbnail their photos, but those photos
+   *  are excluded from cross-cutting views (All Photos, Map, Tags,
+   *  People, Search, sidebar counts). Navigating directly into the
+   *  folder still shows them. Propagates to every descendant folder. */
+  setHidden: async (folderId: string, hidden: boolean) => {
+    const response = await api.post(`/folders/${folderId}/hide`, {
+      hidden,
+    })
+    return response.data as {
+      id: string
+      name: string
+      path: string
+      is_hidden: boolean
+    }
+  },
+
   /** Delete a folder. mode=discard moves all photos under it to the
    *  discard pile (recoverable) and leaves the folder + on-disk dir
    *  alone. mode=permanent unlinks files, removes folder rows, and