Sign in with Google or any OIDC provider

Hive now supports OpenID Connect login. Configure Google as a built-in provider with HIVE_GOOGLE_CLIENT_ID and HIVE_GOOGLE_CLIENT_SECRET, or point a generic provider at its OIDC issuer with HIVE_OIDC_ISSUER. Multiple providers can be enabled side by side, each appearing as its own button on the login page, and optional email-domain allowlists keep access restricted to approved organizations.