Add Request Validation Middleware

[Abd-Standard]

Description:
Introduce centralized validation for incoming API requests before they reach business logic.

Acceptance Criteria:

Invalid payloads are rejected consistently.
Validation errors use a standard response format.
Existing valid requests remain compatible.

[Obaara293]

@Obaara293 has applied to work on this issue as part of the Stellar Wave Program's 9th wave.

Hi maintainer, I've reviewed the issue and I've recognized the solution, kindly assign this to me to get the best result.

ℹ️ Repo Maintainers: To accept this application, review their application or assign @Obaara293 to this issue.

[whiteghost0001]

@whiteghost0001 has applied to work on this issue as part of the Stellar Wave Program's 9th wave.

i would love to work on this issue and summit pr within 2 days

ℹ️ Repo Maintainers: To accept this application, review their application or assign @whiteghost0001 to this issue.

[drips-wave]

Congratulations, @whiteghost0001! 🎉 Your application was accepted by the repo's maintainers, and the issue is due on September 30, 2026.

🧑‍💻 @whiteghost0001: 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 🌊