[Feature]: Favorites and pinned files and folders

Problem

As a user collects more files and folders, the important ones get harder to reach. Every visit starts from the root, and there is no way to keep frequently used folders, notes, or documents one click away. A workspace needs a fast path back to the things a user actually cares about.

Example: a user has a deep folder they open every day. Today they navigate into it manually each time. They should be able to mark it as a favorite and reach it instantly from a favorites area.

Proposed solution

Let users favorite (pin) files and folders and surface those favorites for quick access.

Scope:

• an action to add or remove a file or folder from favorites (from the listing and from the file viewer sidebar, Vault-Web/cloud-page#98)
• persist favorites as per-user metadata, scoped to the owning user
• a favorites view or section that lists the user's pinned items with a direct link to open them
• keep favorites consistent when the underlying item is renamed, moved, or deleted (a deleted item should not linger as a broken favorite)
• respect the existing path validation and user boundary

Acceptance criteria

• A user can mark and unmark files and folders as favorites.
• Favorites are stored per user and are only visible to that user.
• A favorites view lists the user's pinned items and links straight to them.
• Renaming or moving a favorited item keeps the favorite valid; deleting it removes the favorite.
• Favorites never reference items outside the user root.
• The feature has test coverage for add, remove, and user isolation.

Related: the favorite action fits naturally into the file viewer sidebar (Vault-Web/cloud-page#98).