New document hub for centralized file storage — replaces scattered
drives and USB sticks for non-technical SMBs. Three new tables:
storage_folder (nested hierarchy), storage_folder_permission (role
and user-level access control), storage_file.
Backend: folder CRUD with nested paths, file upload/download via
signed URLs, permission checks (view/edit/admin with inheritance
from parent folders), public/private toggle, breadcrumb navigation,
file search.
Frontend: two-panel file manager — collapsible folder tree on left,
icon grid view on right. Folder icons by type, file size display,
upload button, context menu for download/delete. Breadcrumb nav.
Files sidebar link added.