Add conservative trace structure cleanup

[March-77]

Summary

• add a standard-library trace structure checker with separate check and fix modes
• detect duplicate {file, line, code} nodes and same-file boundary anomalies
• support integer and range line values without sorting cross-file traces
• default fixes to verify=0; conflicting duplicate descriptions and verified entries remain review-only
• include generated fixed JSONL, detailed CSV log, aggregate report, documentation, and tests

Dataset results

• 408 entries and 2,073 trace nodes scanned
• 7 duplicate candidates
• 139 before-entry and 217 after-critical candidates
• 382 cross-file nodes retained without line comparison
• 4 clear verify=0 out-of-bounds nodes removed
• 359 events retained for human review
• output remains 408 rows and passes schema smoke checks

Validation

• python -m unittest discover -s tests -p "test_trace_structure_cleanup.py" -v (8 tests)
• python -m py_compile scripts/trace_structure_cleanup.py
• full generated-output schema smoke check
• git diff --check

Closes #5