feat(multisig): implement time-locked multisig policies in builder UI and CLI

[ibrahimmujidah1-stack]

Summary

Implements time-locked multi-signature policies for delayed execution and governance safety:

• Time-Lock Policy Engine (\src/utils/multisig_builder.rs):
  • Adds \TimelockPolicy\ (\min_delay_seconds, \execution_window_seconds, \unlock_at, \expires_at) to \Proposal.
  • Implements \ imelock_status()\ evaluating current execution state (\CollectingSignatures, \Locked, \ReadyToExecute, \Expired).
  • Implements \can_execute()\ checking signature thresholds, validity periods, and mandatory timelock delays.
• CLI Flags & Enforcement (\src/commands/multisig_builder.rs):
  • \starforge multisig create: Added --timelock-delay \ and --execution-window .
  • \starforge multisig view\ & \status: Displays timelock parameters, unlock dates, and execution countdowns.
  • \starforge multisig is-ready\ & \submit: Enforces \can_execute()\ to prevent premature submissions before timelock expiry.
• Unit Tests: Full test suite covering locked proposals, execution eligibility after delay, and expiration outside execution windows.
• Documentation (\docs/TIMELOCKED_MULTISIG.md): Reference guide on timelock policies, states, and CLI usage.

Closes #768

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