Route host changes through the selected Caddy provider, add auth routes
and the frontend-dir serving toggle, seed a default admin user on first
run, and validate space/comma separated domain lists via a custom
validator. Includes validator tests.
Support CPM_AUTH_MODE=local|oidc. OIDC uses go-oidc with JIT user
provisioning and an optional email-domain allowlist. Adds auth config,
login and callback endpoints, a JWT signing-key bootstrap and
Provider/Subject fields on the user model. Includes OIDC allowlist tests.
