refactor: simplify after self-review

- drop the redundant isLoadingMore boolean from the background-loading
  store; derive from inFlight > 0 in the selector
- pull _active_source_root_paths out of get_library_stats and reuse it
  from get_duplicate_groups (same is_active + admin-scope check, now
  in one place)
- drop p.rstrip('/') in the duplicates folder-scope filter (SourceRoot
  paths are never written with a trailing slash)
- match Timeline's initial-load affordance to the new bottom indicator
  (Loader2 spinner + ellipsis instead of plain "Loading photos...")
- trim narrative comments that explained what the surrounding code does

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

backend/app/routers/library.py

@@ -34,6 +34,17 @@ def _owner_filter(user: User, scope: str | None):
         return sa_true()
     return Photo.user_id == user.id
 
+
+async def _active_source_root_paths(
+    db: AsyncSession, user: User, scope: str | None
+) -> list[str]:
+    """Active SourceRoot.path values visible to this user, honouring the
+    admin ?scope=global escape hatch."""
+    q = select(SourceRoot.path).where(SourceRoot.is_active.is_(True))
+    if not (scope == "global" and user.role == "admin"):
+        q = q.where(SourceRoot.user_id == user.id)
+    return (await db.execute(q)).scalars().all()
+
 # Media types we accept in the regenerate-thumbnails request body. Mirrors
 # the values produced by `app.tasks.scan.get_media_type`.
 _VALID_MEDIA_TYPES = {'photo', 'raw', 'heic', 'video'}
@@ -114,15 +125,7 @@ async def get_library_stats(
 
     size = (await db.execute(select(func.sum(Photo.file_size)).where(owner))).scalar() or 0
 
-    # Source root directories (active ones only). Scoped to the
-    # requesting user unless they're an admin asking for global view —
-    # otherwise the Settings panel would leak other users' NC paths.
-    sr_query = select(SourceRoot.path).where(SourceRoot.is_active.is_(True))
-    if not (scope == "global" and current_user.role == "admin"):
-        sr_query = sr_query.where(SourceRoot.user_id == current_user.id)
-    roots = (
-        await db.execute(sr_query.order_by(SourceRoot.path))
-    ).scalars().all()
+    roots = sorted(await _active_source_root_paths(db, current_user, scope))
 
     return {
         "all_photos": all_photos_count,
@@ -731,28 +734,18 @@ async def get_duplicate_groups(
     """
     owner = _owner_filter(current_user, scope)
 
-    # Restrict to photos that actually live under an active SourceRoot
-    # in the user's settings. The folder→source_root link alone is not
-    # enough: Nextcloud's "move to trash" flow can leave a Folder row at
-    # a path like `…/files/.delete/purge-1` still wired to the original
-    # source_root_id, which then leaks its photos into the duplicates
-    # view even though that path is outside everything the user
-    # configured. Filtering on the folder's path being a descendant of
-    # the active root's path matches what the user actually expects to
-    # see in Settings → Source folders.
-    sr_path_query = select(SourceRoot.path).where(SourceRoot.is_active.is_(True))
-    if not (scope == "global" and current_user.role == "admin"):
-        sr_path_query = sr_path_query.where(SourceRoot.user_id == current_user.id)
-    active_root_paths = (await db.execute(sr_path_query)).scalars().all()
+    # Restrict to photos under an active SourceRoot in the user's
+    # settings. Folder.source_root_id alone isn't trustworthy: Nextcloud's
+    # "move to trash" flow leaves Folder rows like `…/files/.delete/
+    # purge-1` still wired to the original source_root_id, leaking their
+    # photos into this view as ghost paths the user never configured.
+    active_root_paths = await _active_source_root_paths(db, current_user, scope)
     if not active_root_paths:
         return {"groups": [], "total_groups": 0, "total_members": 0}
 
-    # Match the source root path itself OR a strict child (path + '/').
-    # `startswith` alone would accept `/files/Photos2` for a `/files/Photos`
-    # root.
     folder_in_scope = or_(
         *[
-            (Folder.path == p) | (Folder.path.like(p.rstrip('/') + '/%'))
+            (Folder.path == p) | (Folder.path.like(p + '/%'))
             for p in active_root_paths
         ]
     )