Add a `wallet rotate --backup` or key history feature

[Nanle-code]

Extend wallet rotation to preserve the previous keypair or export a backup snapshot before generating a new key. Include a clear workflow for safely rotating live accounts while retaining rollover information.

[martoniel]

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

Good day Big Dev! Pls I would love to work on this issue carefully and make PR within 24hrs

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

[drips-wave]

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

🧑‍💻 @martoniel: 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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