Add backup metadata tracking table for exports

[nanaf6203-bit]

Track export and backup jobs with metadata in the database.

Acceptance Criteria:

• Migration adds a backup metadata table.
• Job entries store status, timestamps, and file references.
• Admin endpoints query backup history.
• Tests verify metadata persistence.

[goldandrew]

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

Hi Maintainer, I’d like to take this issue. I will add the migration, job metadata tracking, admin query endpoints, and tests to ensure persistence works correctly.

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

[nafiuishaaq]

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

Hello maintainer, I would like to work on this issue

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

[drips-wave]

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

🧑‍💻 @nafiuishaaq: 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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[drips-wave]

This issue has been completed by @nafiuishaaq as part of the Stellar Wave Program's 6th Wave 🥳

😎 @nafiuishaaq: You earned 150 Points for completing this issue! After the current Wave ends, you'll be eligible for a percentage of the Wave's reward pool based on the percentage of total points you've earned. Learn more here. You can also Leave a review to share your experience working on this issue.

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