New Flask blueprint at /openapi/v1/ that will host user-scoped
programmatic endpoints (device flow, identity, sessions, workspaces).
Ships only a smoke route GET /openapi/v1/_health for now; subsequent
phases lift handlers in from service_api, console, and the orphan
oauth_device_sso.py.
CORS is intentionally omitted here and configured in step A.5 once
the allowlist envvar lands.
Plan: docs/superpowers/plans/2026-04-26-openapi-migration.md (in difyctl repo).