feat(views): saved-views backend — table, model, CRUD + reorder API

Per-user named snapshots of the feed's FeedFilters. New saved_views table
(migration 0035, unique per user+name, position, is_default) + SavedView
model, and a /api/saved-views router (list/create/patch/delete/reorder)
gated behind require_human so the shared demo account can't pollute it.
Setting is_default clears the flag on the user's other views (one default).

backend/app/main.py

@@ -38,6 +38,7 @@ from app.routes import (
     notifications,
     playlists,
     quota,
+    saved_views,
     scheduler as scheduler_routes,
     search as search_routes,
     setup as setup_routes,
@@ -120,6 +121,7 @@ app.include_router(notifications.router)
 app.include_router(messages.router)
 app.include_router(channels.router)
 app.include_router(playlists.router)
+app.include_router(saved_views.router)
 app.include_router(admin.router)
 app.include_router(config_routes.router)
 app.include_router(scheduler_routes.router)