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>

backend/app/routers/library.py

@@ -42,22 +42,26 @@ async def get_library_stats(db: AsyncSession = Depends(get_db)):
       - discarded:    is_discarded = true
       - total_size:   raw bytes across every row, including discarded
     """
-    not_discarded = Photo.is_discarded.is_(False)
+    # Every sidebar badge runs against this filter. `not_visible` is the
+    # inverse: a photo is visible iff it's neither discarded nor hidden
+    # (marked hidden-from-views via a folder toggle). Kept as a single
+    # expression so every sub-count below applies it identically.
+    visible = (Photo.is_discarded.is_(False)) & (Photo.is_hidden.is_(False))
 
     all_photos_count = (
-        await db.execute(select(func.count(Photo.id)).where(not_discarded))
+        await db.execute(select(func.count(Photo.id)).where(visible))
     ).scalar() or 0
 
     rated_count = (
         await db.execute(
-            select(func.count(Photo.id)).where(not_discarded, Photo.rating >= 1)
+            select(func.count(Photo.id)).where(visible, Photo.rating >= 1)
         )
     ).scalar() or 0
 
     colored_count = (
         await db.execute(
             select(func.count(Photo.id)).where(
-                not_discarded, Photo.color_label.is_not(None)
+                visible, Photo.color_label.is_not(None)
             )
         )
     ).scalar() or 0
@@ -65,7 +69,7 @@ async def get_library_stats(db: AsyncSession = Depends(get_db)):
     with_gps_count = (
         await db.execute(
             select(func.count(Photo.id)).where(
-                not_discarded, Photo.latitude.is_not(None)
+                visible, Photo.latitude.is_not(None)
             )
         )
     ).scalar() or 0
@@ -73,7 +77,7 @@ async def get_library_stats(db: AsyncSession = Depends(get_db)):
     duplicates_count = (
         await db.execute(
             select(func.count(Photo.id)).where(
-                not_discarded, Photo.is_duplicate.is_(True)
+                visible, Photo.is_duplicate.is_(True)
             )
         )
     ).scalar() or 0
@@ -721,6 +725,7 @@ async def get_duplicate_groups(db: AsyncSession = Depends(get_db)):
             )
             .where(Photo.duplicate_group_id.is_not(None))
             .where(Photo.is_discarded.is_(False))
+            .where(Photo.is_hidden.is_(False))
             .order_by(Photo.duplicate_group_id)
         )
     ).all()