feat: implement multi-admin and multisig support for governance

[greatest0fallt1me]

Description:

Support multiple admin addresses and optional threshold (multisig) so that sensitive operations require M-of-N admin signatures.

Requirements and Context:

• Must be secure, tested, and documented
• Should allow adding/removing admins (by existing admin or current multisig)
• Should allow setting threshold (e.g., 2 of 3) for admin actions
• Should require threshold to be met for pause, fee withdrawal, upgrade, etc.
• Should emit events for admin and threshold changes
• Must not break single-admin deployment (1 admin, threshold 1)
• Should document multisig flow and Soroban auth patterns

Suggested Execution:

1. Fork the repo and create a branch

   git checkout -b feature/multi-admin-multisig

2. Implement changes

   • Write contract: admin set, threshold, and auth checks in admin functions
   • Add admin module: src/admin.rs (multi-admin and threshold logic)
   • Update storage and events; add documentation and NatSpec-style comments

3. Test and commit

   • Run tests; cover single admin, multi-admin, threshold enforcement
   • Include test output and security notes

Example Commit Message:

feat: implement multi-admin and multisig support for governance

Guidelines:

• Minimum 95 percent test coverage
• Clear documentation
• Timeframe: 96 hours

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[ayomideadeniran]

@ayomideadeniran has applied to work on this issue as part of the Stellar Wave Program's 2nd wave.

I'm a full-stack developer and I'd like to take this issue.
I understand the requirements and will follow the existing project structure, keep the implementation clean, and include proper tests where applicable.

ETA: 1–3 days (depending on scope)
Portfolio: https://knightsdev-portfolio.vercel.app/

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

[drips-wave]

Congratulations, @ayomideadeniran! 🎉 Your application was accepted by the repo's maintainers, and the issue is due on February 26, 2026.

🧑‍💻 @ayomideadeniran: 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.

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