Add monitoring/alerting for failed Stellar transaction submissions

[Codex723]

Summary

Set up alerting (e.g. via the observability stack above) when the rate of failed /api/stellar/submit calls crosses a threshold, indicating a possible network or integration issue.

Difficulty

Advanced — estimated effort: ~3-7 days (may need discussion before starting). Labels: backend, observability, advanced

Where to Work

• /api/stellar/submit

How to Approach This

1. Locate the relevant file(s) below under src/app/api/ or src/lib/.
2. Check src/lib/api-response.ts and follow its existing success/error response shape — don't invent a new one.
3. If you're touching validation, add/extend a Zod schema in src/lib/validations.ts rather than validating inline.
4. If the change affects the database, check prisma/schema.prisma first and run npx prisma generate after any schema edit.
5. Add or update tests near the affected route/lib file (create a __tests__ folder alongside it if one doesn't exist yet, matching the project's existing test conventions).
6. Manually verify with npm run dev and a tool like curl or Postman/Insomnia against the affected endpoint before opening a PR.

Acceptance Criteria

• Behavior described above is implemented in the file(s) listed under "Files Likely Affected".
• Response shape follows the existing convention in src/lib/api-response.ts.
• Input validation (if applicable) is added via src/lib/validations.ts, not inline.
• Tests added/updated covering both the happy path and at least one failure/edge case.
• Manually verified against a running local server (npm run dev).
• No new TypeScript or lint errors (npm run lint, tsc --noEmit).

Notes for Contributors

Comment on this issue before starting so it can be assigned to you and duplicate work is avoided. If the described approach doesn't quite fit once you're in the code (e.g. the file has moved, or there's a cleaner way to do it), that's fine — leave a comment explaining the deviation in your PR description rather than silently changing scope.