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).
