#437 Missing oauth2_platform.py module causes startup warning

The api/app.py imports api.oauth_handlers.oauth2_platform.platform_auth_bp but the module was never created. Added in commit 822f18e8 (Nov 24 'going to fix issues') but implementation incomplete. Every API startup shows: 'Platform auth module not found'. Either implement the module for enterprise SSO or remove the import if not needed.