fix(dead-code): count JSX prop function references as usage (closes #294)

[Wolfvin]

Root cause

.tsx files are parsed by parsers/tsx_parser.py (TSXParser, routed from commands/scan.py:711) — NOT ts_backend_parser.py. Its tree walk emitted CALLS edges only for call_expression / new_expression / JSX component elements. A function passed as a JSX prop value (onClick={handleClick}) is a bare identifier inside a jsx_expression container — a reference, not a call — so it produced zero edges. ref_count is computed from incoming edges, so every React event handler got rc=0 / status=dead (mass false-positive on the primary React use case).

Fix

scripts/parsers/tsx_parser.py — new _process_jsx_expression, dispatched from the tree walk on jsx_expression nodes. It emits a usage edge (via_jsx_ref) from the enclosing function to a referenced name, but ONLY when that name resolves to a function declared in the same file (declared guard) — arbitrary identifiers / DOM props / non-function names are never counted. Two shapes handled:

1. Attribute/child reference: onClick={handleClick} (direct identifier).
2. Callback argument: {items.map(renderItem)} (identifier in a call's arguments).

Double-counting avoided: the function position of a call_expression is skipped (already emitted by _parse_call), nested jsx_expression nodes are left to the outer walk, and member_expression (items.map, this.x) is skipped.

Before / after (repro from the issue)

fn	before	after
handleClick (onClick={handleClick})	rc=0 dead	rc=1 active
handleSubmit (onSubmit={handleSubmit})	rc=0 dead	rc=1 active
renderItem ({items.map(renderItem)})	rc=0 dead	rc=1 active
directlyCalled (directlyCalled())	rc=1 active	rc=1 active (no regress)
reallyUnused / unusedHandler (control)	rc=0 dead	rc=0 dead (still dead)

Tests

Added 4 golden assertions + a App.tsx fixture to tests/test_graph_accuracy_golden.py: JSX-prop handler rc>=1, callback-arg rc>=1, direct-call not regressed, genuinely-unused handler still dead.

Wide-net run (all pass):

pytest tests/test_graph_accuracy_golden.py tests/test_graph_model.py tests/test_deadcode_engine.py tests/test_dead_code_command.py
63 passed

Also green: test_ts_backend_parser.py, test_js_backend_parser.py.

🤖 Generated with Claude Code

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[sonarqubecloud]

Quality Gate passed

Issues
2 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

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