Consistent response envelope format

Inconsistent response envelopes — some routes returning { data: ... }, others returning raw objects, others using { success: true, result: ... } — force every API consumer to write bespoke error-handling logic per endpoint. This violates ISO-25010:2011 compatibility.interoperability and means a new integration can silently swallow errors that use the wrong shape. In practice, it produces bugs where a frontend assumes data is present but the route returned the payload at root level.

Define a shared response helper at src/lib/api-response.ts and replace all direct Response.json() calls with it:

// src/lib/api-response.ts
export const apiSuccess = <T>(data: T, status = 200) =>
  Response.json({ data }, { status })

export const apiError = (code: string, message: string, status: number) =>
  Response.json({ error: { code, message } }, { status })

Success responses always carry { data: <payload> }; error responses always carry { error: { code, message } }. Import and use these in every route handler. This gives clients a single shape to handle and gives you a single place to add observability later.