feat(backend): propagate X-Request-ID header on all responses using requestContext.ts

[Dev-AdeTutu]

Summary

requestContext.ts already generates per-request IDs but they are never sent back in the response. Attaching X-Request-ID to every response makes distributed tracing and client-side error reporting much easier.

Acceptance Criteria

• Every HTTP response includes X-Request-ID: <uuid>
• The ID is either taken from the incoming X-Request-ID header (if present) or generated fresh
• Middleware logs the request ID alongside method and path
• Works via requestLogger.ts or a new standalone middleware

Files to touch

• backend/src/lib/requestContext.ts
• backend/src/middleware/requestLogger.ts

[Oluwasuyi-Oluwatimilehin-Daniel]

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

Hello maintainer, please assign me to this task. i would get started immediately
ETA 1hour

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