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.

internal/app/auth.go

@@ -100,6 +100,10 @@ func (a *App) getUser(user, pass string) (u *User) {
 		raw := users.Get([]byte(user))
 		if raw != nil {
 			json.Unmarshal(raw, &u)
+			if u.Pass == nil {
+				u = nil
+				return nil
+			}
 			if bcrypt.CompareHashAndPassword(u.Pass, []byte(pass)) != nil {
 				u = nil
 				return nil