Feature Request: Support login_hint Parameter for SSO OAuth Authorization Requests

Summary Add support for passing the OpenID Connect / OAuth 2.0 login_hint parameter when Vaultwarden initiates authentication requests to an external SSO provider. Use Case Many identity providers support the optional login_hint parameter on the /authorize endpoint. This allows the client application to provide a suggested username, email address, or account identifier to the IdP, improving the user experience by: • Pre-filling the username field on the login page. • Helping users with multiple accounts select the correct identity. • Reducing friction during re-authentication flows. • Supporting IdP-specific account routing and home realm discovery features. Proposed Behavior When redirecting users to the OAuth/OIDC authorization endpoint, Vaultwarden could optionally include: The value could be sourced from: • The email address entered on the Vaultwarden login page before SSO redirection. • A configurable template or…