The OOBE flow on the web portal calls this endpoint to create a fresh
`clients` row bound to the Better Auth user's email when the SSO
bridge returns 404. Returns 201 on success, 409 if a client with that
email already exists (portal-selection case), 401/503 on auth issues,
400 on invalid body.
The OOBE success path navigates the user back to `/` and lets the
existing `session-from-auth` re-bridge; the new client is now
resolvable by email, so the bridge mints a real portal session.
Tests cover: 401 (no session), 400 (zod), 201 + persisted values
(name trimmed, optional fields normalized to null), 409 (existing
client or unique-constraint race), 503 (auth not configured).
Paired with the web PR on `feature/2357-p2-sso-to-oobe-routing`.
Co-Authored-By: Paperclip <noreply@paperclip.ing>
Flea Flicker
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