Adds an optional displayName claim to the platform access token so
downstream product backends can source the user's display name from the
JWT (single source of truth = platform auth), not from per-product DB
copies. verifyToken already exposes displayName; this populates it at all
token-minting sites (password login, register, refresh, SSO, OAuth,
magic-link, passkeys, QR, enterprise SAML/OIDC). Additive and backward
compatible.
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>