Admin Action Timelock (2-Day Delay)

[Luluameh]

Background
Rushed or malicious admin actions (e.g., changing platform fees dramatically) can harm users. A timelock gives the community time to react.
Goal
Wrap critical admin functions with a 2-day timelock. Proposed actions are queued and must be executed after the delay expires.
Acceptance Criteria

• DataKey::PendingAction(action_hash) stores { action, proposed_at }.
• propose_admin_action(action_payload) stores the pending entry.
• execute_admin_action(action_hash) checks ledger_time >= proposed_at + 172800.
• Returns Error::TimelockActive if too early.
  Key Files
  contracts/src/admin.rs, contracts/src/timelock.rs