Implement OAuth login functionality and enhance documentation

- Added support for Google OAuth login, including new API endpoints for OAuth providers and callbacks.
- Updated user authentication logic to handle OAuth-only users.
- Enhanced README.md and deployment documentation with OAuth setup instructions.
- Modified frontend components to include OAuth login options and improved error handling.
- Updated configuration files to include new environment variables for OAuth integration.

README.md

@@ -28,6 +28,10 @@ Only other thing you need to do is setup users and set your zero grid.
 
 First login: username **admin**, password from `HNHMAP_BOOTSTRAP_PASSWORD` (in dev Compose it defaults to `admin`). Go to the admin portal and hit "ADD USER".  Don't forget to toggle on all the roles (you'll need admin, at least)
 
+### OAuth (Google)
+
+To enable "Login with Google", set `HNHMAP_OAUTH_GOOGLE_CLIENT_ID`, `HNHMAP_OAUTH_GOOGLE_CLIENT_SECRET`, and `HNHMAP_BASE_URL` (your app's full URL). Create OAuth credentials in Google Cloud Console and add the callback URL `{HNHMAP_BASE_URL}/map/api/oauth/google/callback` to Authorized redirect URIs. See [deployment.md](docs/deployment.md) for details.
+
 Once you create your first user, you'll get kicked out and have to log in as it.
 The admin user will be gone at this point.  Next you'll want to add users for anyone else, and then you'll need to create your tokens to upload stuff.