auth: show user profile in `auth status` via core GET /me

entire auth status now calls the core API's GET /me, which both validates the stored token (liveness) and supplies a profile header:

Logged in to https://us.auth.entire.io User: Alice Smith (@alice) alice@example.com Identity: github/alice Token: stored in OS keychain

Active sessions: ...

/me is the primary liveness gate (a 401 surfaces as *coreapi.ErrorModelStatusCode, now recognised by isKeychainTokenRejected). The active-sessions list runs after, on the data API; since the token is already known good, a list failure degrades to a stderr warning instead of failing the command. Empty profile fields are omitted.