[Contracts] Implement Upgradeable Smart Contract pattern

[ONEONUORA]

Description

Implement the upgrade pattern to support future contract logic updates:

• Write the upgrade entrypoint.
• Swap contract WASM hash on-chain using Soroban host functions.

Acceptance Criteria

• Protected by strict admin credentials.
• Retains persistent storage variables after upgrades.
• Tested upgrade scenarios.

[Blaqkenny]

@Blaqkenny has applied to work on this issue as part of the Stellar Wave Program's 6th wave.

hello maintainer, please can i work on this issue and give you a better result

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

[grantfox-oss]

🦊 GrantFox — @Blaqkenny has been assigned to this issue as part of the Official Campaign campaign!

Next steps:

1. Open a Pull Request referencing this issue (e.g., Closes #838)
2. Your PR will be reviewed by the Fracverse maintainers

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[drips-wave]

Congratulations, @Blaqkenny! 🎉 Your application was accepted by the repo's maintainers, and the issue is due on June 30, 2026.

🧑‍💻 @Blaqkenny: 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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