- Implement transitive_closure(): computes full dependency tree for each node
- Implement find_deep_chains(): identifies longest paths in dependency graph
- JSON output now includes `transitive` and `deep_chains` fields
- Added comprehensive unit tests in scripts/test_dependency_graph.py (9 tests)
- Handles cycles correctly, excludes self-references from closure
Meets acceptance criteria for #111:
✅ Builds transitive dep tree
✅ Identifies deep chains and circular deps
✅ Output: transitive dependency graph (via --format json)
Closes#111
