Add a standardized error-response contract across API routes

[robertocarlous]

Why
The backend already has structured middleware and request IDs, but response bodies can still vary by route. A standardized error shape would make integrations and client handling more predictable.

Acceptance criteria

• Define one canonical error response format.
• Apply it consistently across auth, admin, analytics, and public routes.
• Document the format and include examples for 400, 401, 403, 404, and 500 responses.

[directorfloo]

i will love to work on this issue

[Menjay7]

Hi! I came across this issue and would love to work on it. I have experience with similar tasks and I'm confident I can investigate, implement a clean solution, and thoroughly test it before submitting a PR. If the issue is still open, I would appreciate it if you could assign it to me. Thank you!

[Tobi-8]

oh, i have done this exact same thing before.
kindly assign