Unify API error envelopes across route handlers

[Abidoyesimze]

API routes return inconsistent error JSON shapes.

Affected files

• src/app/api/**/route.ts
• src/lib/api-response.ts

Tasks

• Use api-response helpers for all error paths.
• Standardize { error: { code, message } } (or documented contract).
• Update client fetch code to parse the unified shape.

Acceptance criteria

• Scope is limited to the files listed (or agreed alternatives in the PR).
• Change is verifiable: tests, screenshots, or written QA steps in the PR.
• No behavior regressions in related user flows.
• No new duplicate abstractions without a one-line rationale in the PR.

Suggested labels

cleanup, api, refactor

Notes

Standalone cleanup issue from CLEANUP_ISSUES_2026-05.md. Complements the audit queue and product backlog.

[icentedward76-sketch]

@icentedward76-sketch has applied to work on this issue as part of the Stellar Wave Program's 6th wave.

please can i work on this issue

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