The v1 API is here; v0 is now deprecated

We rewrote the API and the new one lives under /api/v1. It has a single error envelope, proper status codes and a real OpenAPI document. The old /api/v0 keeps working for now but is frozen: no new features, and it will be switched off on 30 June. Move your tokens and scripts over; the paths are mostly the same with v1 in place of v0.