[Backend] -- Improve Transaction Search with Saved Queries

[Devsol-01]

Description:
Transaction search becomes more valuable when users can save frequently used filters. Implement saved query creation, listing, and execution.

Acceptance Criteria:

• Saved query CRUD.
• Search executes saved filters.
• RBAC ensures user isolation.

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[Songu3020]

@Songu3020 has applied to work on this issue as part of the Stellar Wave Program's 6th wave.

Hi, I'm Peter — a Full-Stack & Blockchain Developer with 3+ years of experience. I've reviewed this issue and I'm confident I can handle it. I'll submit a clean PR within 1-2 days max. Please assign it to me!

ℹ️ Repo Maintainers: To accept this application, review their application or assign @Songu3020 to this issue.

[drips-wave]

Congratulations, @Songu3020! 🎉 Your application was accepted by the repo's maintainers, and the issue is due on June 30, 2026.

🧑‍💻 @Songu3020: 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

When opening a PR, please link it to this issue to ensure it gets tracked accurately. Points are awarded when this issue is marked as completed by the maintainer.

🤠 Repo maintainers: Please keep an eye on the contributor's progress and review their work before the due date. You can manage this issue, including adjusting its complexity and points, here.

🌊 Happy Wave 🌊

[drips-wave]

This issue has been marked as completed by a Drips Wave moderator for @Songu3020 as part of the Stellar Wave Program's 6th Wave 🥳

Moderator's reason: [Auto-assessed] The PR was merged by a maintainer and provides comprehensive unit tests covering all acceptance criteria mentioned in the issue, including CRUD operations and RBAC isolation. Although the diff only shows test file changes, the merge status confirms the maintainer is satisfied with the contribution as a resolution for the issue.

😎 @Songu3020: 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.

🧑‍💻 Repo maintainers: How'd the contributor do? Leave a review to share your experience working with them.

ℹ️ Note: This issue was marked complete via moderation. Points were issued even though the GitHub issue remains open.