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/project_manager.py

@@ -14,6 +14,7 @@ from plugins import BasePlugin, registry
 
 logger = logging.getLogger(__name__)
 
+
 class ProjectManager:
     """
     Manage multiple project instances.
@@ -233,9 +234,11 @@ class ProjectManager:
             for full_id, plugin in self.projects.items()
         ]
 
+
 # Global project manager instance
 _project_manager: ProjectManager | None = None
 
+
 def get_project_manager() -> ProjectManager:
     """Get the global project manager instance."""
     global _project_manager