Consistent API naming convention

Inconsistent API naming erodes maintainability (ISO-25010:2011 maintainability.modifiability): a mix of kebab-case, camelCase, and plural/singular resource names forces every developer to read each route individually rather than predicting it. Client codebases accumulate one-off special cases for each naming quirk, and search-and-replace migrations become unreliable. When AI generates new routes or a second engineer adds an endpoint, the inconsistency compounds — each addition makes the surface harder to audit and the refactor more expensive.

Pick one convention — lowercase kebab-case with plural resource names is the REST standard — and rename every route directory or file to match. In Next.js App Router, route names are directory names, so the rename is mechanical:

app/api/v1/users/route.ts
app/api/v1/user-profiles/route.ts
app/api/v1/billing-invoices/route.ts

Update every client-side fetch call in the same commit. Add a one-paragraph convention note to your README or an api-conventions.md file so contributors don't reintroduce drift. Internal-namespace routes (e.g., /api/cron/) are fine as a separate prefix only when that separation is documented.