Multi-user sharing, groups, and in-app notifications

Backend:
- Alembic migration 0025: groups, group_memberships, project_shares,
  note_shares, notifications tables
- models: Group, GroupMembership, ProjectShare, NoteShare, Notification
- services/access.py: permission resolution (viewer/editor/admin/owner)
- services/groups.py + routes/groups.py: full group CRUD + membership
- services/sharing.py + routes/shares.py: project/note sharing API
- services/notifications.py: in-app notification create/list/mark-read
- routes/in_app_notifications.py: GET/POST notification endpoints
- routes/users.py: user search endpoint
- services/projects.py + services/notes.py: *_for_user variants
- routes updated to use *_for_user on get/list; adds permission field
- app.py: register all new blueprints

Frontend:
- api/client.ts: ShareEntry, GroupEntry, NotificationEntry types + helpers
- stores/notifications.ts: Pinia store with polling
- NotificationBell.vue: bell icon + badge + dropdown toggle + 60s poll
- NotificationsPanel.vue: unread notification list with mark-all-read
- ShareDialog.vue: teleport modal for sharing projects/notes with users/groups
- SharedWithMeView.vue: /shared route listing shared projects and notes
- AppHeader: NotificationBell, Shared nav link
- ProjectView, NoteViewerView, TaskViewerView: Share button + ShareDialog
- SettingsView: Groups admin tab with create/delete groups + member mgmt
- router: /shared route

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/fabledassistant/services/notes.py

@@ -441,3 +441,20 @@ async def build_note_graph(
                 edges.append({"source": nid, "target": tag_node_id, "type": "tag"})
 
     return {"nodes": nodes, "edges": edges}
+
+
+# ---------------------------------------------------------------------------
+# Shared-access variant
+# ---------------------------------------------------------------------------
+
+async def get_note_for_user(
+    accessing_user_id: int, note_id: int
+) -> tuple["Note", str] | None:
+    """Returns (note, permission) if user has any access, else None."""
+    from fabledassistant.services.access import get_note_permission
+    perm = await get_note_permission(accessing_user_id, note_id)
+    if perm is None:
+        return None
+    async with async_session() as session:
+        note = await session.get(Note, note_id)
+    return (note, perm) if note else None