New REFERENCES edge type

[geeknik]

Helps mitigate #160 with new REFERENCES edge type.

The parser now detects function-as-value references — identifiers in value positions that refer to functions without directly calling them. This covers the most common static patterns that cause false positives in dead code detection.

Patterns detected (JS/TS and Python):

  ┌───────────────────────┬───────────────────┐
  │        Pattern        │      Example      │
  ├───────────────────────┼───────────────────┤
  │ Object literal values │ { handler: myFn } │
  ├───────────────────────┼───────────────────┤
  │ Shorthand properties  │ { myFn }          │
  ├───────────────────────┼───────────────────┤
  │ Property assignments  │ map['key'] = myFn │
  ├───────────────────────┼───────────────────┤
  │ Array/list elements   │ [fn1, fn2, fn3]   │
  ├───────────────────────┼───────────────────┤
  │ Callback arguments    │ register(myFn)    │
  ├───────────────────────┼───────────────────┤
  │ Python dict values    │ {'key': my_fn}    │
  └───────────────────────┴───────────────────┘

Files modified:

• code_review_graph/parser.py — Added _extract_value_references method with 5 sub-extractors (_ref_from_pair, _ref_from_assignment, _ref_from_array, _ref_from_arguments, _emit_reference_if_known). Updated _resolve_call_targets to resolve REFERENCES edges. Integrated into _extract_from_tree.
• code_review_graph/refactor.py — find_dead_code now checks for REFERENCES edges. Updated docstring with dynamic dispatch caveats.
• code_review_graph/graph.py — Updated edge kind documentation.
• tests/test_parser.py — 12 new tests in TestValueReferences class.
• tests/test_refactor.py — 4 new tests in TestFindDeadCodeWithReferences class.
• tests/fixtures/sample_map_dispatch.ts — New TS fixture with dispatch patterns.
• tests/fixtures/sample_map_dispatch.py — New Python fixture with dispatch patterns.

Safety constraints:

• Only emits REFERENCES for identifiers that are known (in defined_names or import_map)
• Filters out constants (all-uppercase), single-char names, and language keywords
• Works at both module scope and function scope

Known remaining limitations (documented in docstring):

• Fully dynamic keys (map[computedKey()] = fn) — requires abstract interpretation
• Reflect.apply / Function.prototype.call indirection
• Runtime require() / dynamic import()

[geeknik]

On a small repo I'm working on...
Before: Full build: 32 files, 213 nodes, 1561 edges (postprocess=full)
After: Full build: 37 files, 296 nodes, 2680 edges (postprocess=full)