OIDC login supports multiple providers including Google and generic issuers

Authentication is now delegated to Ueberauth + ueberauth_oidcc, and you can configure one or more OIDC providers at the same time. Out of the box, Google is supported as a first-class provider with HIVE_GOOGLE_CLIENT_ID and HIVE_GOOGLE_CLIENT_SECRET, and any generic OIDC provider can be wired up via HIVE_OIDC_ISSUER plus its .well-known/openid-configuration. Each configured provider appears as its own button on the login page, and the controller routes start/callback flows at /auth/:provider. The README documents the setup for Google Cloud Console and generic providers. Sources: https://github.com/tuist/hive/commit/c3f6e58, https://github.com/tuist/hive/commit/dcccd7b, https://raw.githubusercontent.com/tuist/hive/server%400.1.0/README.md