fix: resolve assigned integration test and CI flakiness issues (#486, #487, #488, #489)

[charlesedeh021-cell]

Closes #486
Closes #487
Closes #488
Closes #489

Summary of Solved Issues

This pull request resolves the four open-source issues assigned to charlesedeh021-cell:

1. /api/notifications Integration Test Coverage (Closes #489)

• Added _tests_/notifications-api.test.ts\ covering GET requests to /api/notifications/[address].
• Verified successful retrieval of user notifications and graceful fallback to an empty array when backing database error occurs.

2. /api/auth Integration Test & Documentation (Closes #488)

• Added _tests_/auth-api.test.ts\ testing SEP-10 authentication endpoints (/api/auth/challenge\ and /api/auth/verify).
• Verified parameter validation, invalid key handling, challenge transaction construction, and JWT token issuance.
• Documented the SEP-10 authentication flow in \docs/architecture.md.

3. /api/reminders Integration Test Enhancements (Closes #487)

• Extended _tests_/reminders.test.ts\ with comprehensive coverage for:
  • Missing field validation (400) and database error handling (500) on POST requests.
  • Authorization check failure (401) on GET cron triggers.
  • Handling Resend API delivery failures gracefully without persisting reminder records.
  • Verifying \List-Unsubscribe\ header structure in outgoing reminder emails.

4. Flaky Test Detection & Quarantine Process (Closes #486)

• Added .github/workflows/flaky-test-detection.yml\ to run the test suite 3x on a weekly schedule (Sundays at 03:00 UTC) to catch intermittent failures.
• Documented the test flakiness tracking and .skip\ quarantine process in \CONTRIBUTING.md.

[drips-wave]

@charlesedeh021-cell Great news! 🎉 Based on an automated assessment of this PR, the linked Wave issue(s) no longer count against your application limits.

You can now already apply to more issues while waiting for a review of this PR. Keep up the great work! 🚀

Learn more about application limits

[Marvell69]

Welldone @charlesedeh021-cell