Add Authorization Boundary Tests

[Abd-Standard]

Description:
Verify that authenticated users cannot access or modify notification resources outside their permitted scope.

Acceptance Criteria:

Cross-user access is rejected.
Resource ownership is validated.
Tests cover both read and write operations.

[Vicolas11]

@Vicolas11 has applied to work on this issue as part of the Stellar Wave Program's 9th wave.

Please assign.

ℹ️ Repo Maintainers: To accept this application, review their application or assign @Vicolas11 to this issue.

[paulddeveloper-droid]

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

I can add authorization boundary tests covering cross-user access, resource ownership, and both read and write operations.

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

[pelumixxril]

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

Let me fix this issue

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

[flare-999]

@flare-999 has applied to work on this issue as part of the Stellar Wave Program's 9th wave.

I'm interested on working on this issue,i have worked on similar issues and delivered good pr.
please assign this to me.

ℹ️ Repo Maintainers: To accept this application, review their application or assign @flare-999 to this issue.

[drips-wave]

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

🧑‍💻 @pelumixxril: 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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