New content_folders table with hierarchical parent_id and per-user
scoping. content.folder_id added (ON DELETE SET NULL so deleting a
folder drops items back to root). New /api/folders route exposes
list/create/rename/move/delete with cycle detection on move.
Content library UI: breadcrumb navigation, subfolder grid, "+ New
Folder" creates inside the current folder, drag-and-drop content
items onto folder cards to move them, and the edit modal has a
folder dropdown showing each folder's full path.
Per-user scoping is enforced server-side: every folder query
filters by user_id, and folder ownership is checked on both folder
mutations and content.folder_id updates.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
