fix(ci): fix black/ruff failures, add CoC and PR template

- Fix Python formatting (sync no longer strips blank lines from .py files)
- Remove test_community_build.py (tests private sync module)
- Fix ruff warnings in test files
- Add CODE_OF_CONDUCT.md
- Add .github/PULL_REQUEST_TEMPLATE.md

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

core/oauth/client_registry.py

@@ -13,6 +13,7 @@ from .schemas import OAuthClient
 
 logger = logging.getLogger(__name__)
 
+
 class ClientRegistry:
     """
     OAuth Client Registry with JSON storage.
@@ -143,9 +144,11 @@ class ClientRegistry:
             return True
         return False
 
+
 # Singleton instance
 _client_registry: ClientRegistry | None = None
 
+
 def get_client_registry() -> ClientRegistry:
     """Get singleton ClientRegistry instance"""
     global _client_registry