Merge branch 'zijie/fix-dist-3': Fix distributed port conflict

- Auto port allocation with _find_free_port() in model_runner.py
- Resource management refactor with close() + context manager in llm_engine.py
- Add tests/test_port_conflict.py and tests/run_parallel_niah.sh
- Remove docs/torch_distributed_port_issue.md (issue fixed)
- Ignore tests/data/ directory

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

.gitignore

@@ -224,3 +224,6 @@ coordination/orchestration/*
 claude-flow
 # Removed Windows wrapper files per user request
 hive-mind-prompt-*.txt
+
+# Test data
+tests/data/