fix: address 7 security and reliability issues

- Prevent path traversal in gitignore template names (Critical)
- Fix TOCTOU races in file operations with try/except pattern (High)
- Add timeout to HuggingFace API requests (Medium)
- Add missing %x00 separator in changelog fallback format (Medium)
- Filter unsanitized kwargs before passing to OpenAI SDK (High)
- Use context managers for proper client cleanup in providers (High)
- Exit with non-zero code on commit engine failure (Low)

devgen/modules/commit_generator.py

@@ -388,6 +388,7 @@ def run_commit_engine(**kwargs: Any) -> None:
         sys.exit(0)
     except Exception as e:
         logger.error(f"Commit engine failed: {e}", exc_info=True)
+        sys.exit(1)
 
 
 __all__ = ["CommitEngine", "CommitEngineError", "run_commit_engine"]