Activate social OAuth in production

register OAuth apps with Google (console.cloud.google.com), Facebook (developers.facebook.com), and GitHub (github.com/settings/developers). Populate GOOGLE_CLIENT_ID, GOOGLE_CLIENT_SECRET, FACEBOOK_APP_ID, FACEBOOK_APP_SECRET, GITHUB_CLIENT_ID, GITHUB_CLIENT_SECRET in .kamal/secrets. Redeploy. No code changes needed – buttons are already rendered and guarded by ENV key presence. Facebook requires Privacy Policy URL (live at /privacy).