[CT-16] Implement proposal creation function

[yusuftomilola]

Overview

Implement the create_proposal function so admin or eligible members can submit governance proposals. Work inside contracts/sandbox/governance/.

Acceptance Criteria

• create_proposal(env, proposer, id, title, description, start_time, end_time) is implemented
• proposer.require_auth() is called
• Validates start_time < end_time
• Returns error if proposal ID already exists
• Stores proposal with Active status
• Indexes proposal ID in ProposalList
• Emits a creation event
• Code compiles with cargo build

[demilade18-git]

@demilade18-git has applied to work on this issue as part of the Stellar Wave Program's 4th wave.

can i work on this?

ℹ️ Repo Maintainers: To accept this application, review their application or assign @demilade18-git to this issue.

[drips-wave]

Congratulations, @demilade18-git! 🎉 Your application was accepted by the repo's maintainers, and the issue is due on April 29, 2026.

🧑‍💻 @demilade18-git: Please resolve the issue such that the repo's maintainers have enough time to review your contribution before the due date. You'll earn Points for completing the issue on-time, which will make you eligible for a share of the Stellar Wave Program's reward pool.

Warning

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[drips-wave]

This issue has been completed by @demilade18-git as part of the Stellar Wave Program's 4th Wave 🥳

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