feat: implement proposal scheduling and timelock in governance contract

[Anuoluwapo25]

After a proposal passes, add a timelock delay before execution to allow time for objections.\n\nContract changes:\n- [ ] Add configurable timelock delay (e.g. 48h)\n- [ ] Transition proposal state: PASSED → QUEUED → EXECUTED\n- [ ] Allow vetoing a queued proposal (admin or supermajority)\n- [ ] Emit ProposalQueued and ProposalExecuted events\n\nFrontend changes:\n- [ ] Show timelock countdown on passed proposals\n- [ ] Show QUEUED status in proposal list

[RaymondAbiola]

@RaymondAbiola has applied to work on this issue as part of the Stellar Wave Program's 5th wave.

Hi, I’d like to work on this issue. I have experience with rust, Solidity, frontend, and backend development, and I’m confident I can deliver a clean solution.

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[DSOTec]

@DSOTec has applied to work on this issue as part of the Stellar Wave Program's 5th wave.

Hi, I would like to work on this issue. Please Kindly assign

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[drips-wave]

Congratulations, @DSOTec! 🎉 Your application was accepted by the repo's maintainers, and the issue is due on June 2, 2026.

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[drips-wave]

This issue has been marked as completed by a Drips Wave moderator for @DSOTec as part of the Stellar Wave Program's 5th Wave 🥳

Moderator's reason: [Auto-assessed] The PR was merged by a maintainer and comprehensively addresses all requirements of the issue, including smart contract state transitions, timelock logic, a veto mechanism, and frontend status updates. Although the issue remains open, the merged status of the PR indicates the contribution was accepted and completed.

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