Locking "closed" tracker items 🔒 (in progress)

Currently, Tiki does not allow locking tracker items, which limits its use in contexts that require immutability — such as invoice management under legal regulations.

This feature introduces a system preference (e.g., tracker_lock_closed_items) that prevents editing tracker items with status "Closed".

Once enabled:

• Users cannot modify locked items through the UI.
• Only trusted roles (e.g., system administrators) can alter these via database access.
• This helps make Tiki more compliant with digital governance standards.