TraceIndex: build queryable TraceLens report catalogs

[ajassani]

Summary

• Add TraceLens_trace_index and a TraceLens.TraceIndex package for building queryable trace report catalogs from many TraceLens reports.
• Split TraceIndex into backend-neutral scanner/importer/model APIs plus a TraceIndexStore interface, with SQLite as the first local backend.
• Document the backend model and cover scan/import/search behavior with synthetic tests.

Test plan

• python -m pytest tests/test_trace_index.py tests/test_copyright_headers.py -q
• python -m TraceLens.TraceIndex.cli --help
• python -m compileall -q TraceLens/TraceIndex
• Remote Linux smoke test: scanned 3 existing trace files, imported an existing TraceLens CSV report directory, and verified search/table counts against the generated index.