[RFC] Enable Supabase OAuth providers in the login/signup page

[pqnet]

Problem

Atomic CRM does not support OAuth/oidc login providers from Supabase

Solution

• add an "OAuthLoginButton" component (shows a single button) and an "OAuthLoginButtons" (shows all enabled providers)
• add an oauthProvider parameter to the login method of the auth provider that allow
• add an environment variable to configure

How To Test

• enable an oauth provider (tested with Google) in the supabase dashboard
• configure the VITE_ENABLED_OAUTH_PROVIDERS variable with a comma separated list of providers (e.g. VITE_ENABLED_OAUTH_PROVIDERS=google)
• build and serve the client, navigate to the signup/login page
• click the "Sign in with xxx" button
• complete auth flow

Additional Checks

• The documentation is up to date
• Tested with fakerest provider (see related documentation)
• Tested with Mobile resolution

[pqnet]

Notes/missing

• Only the google auth path is tested. Remaining is extrapolated from documentation.
• UI is very basic, I just copied the SSOAuthButton component.
• Core functionality written manually (first commit), AI helped with generalization, writing tests, wiring up configuration.
• I'm new to this project so I'm not sure all the possible path are exercised yet. Will test mcp soon.