feat(database): SQLite shadow database for indexed queries
:Release Notes:
- Add ACID-compliant SQLiteStore (WAL mode, FULL sync, FK constraints)
- Add AnomalyType enum for normalized anomaly storage
- Add legacy data migration script (dry-run, batch, rollback)
- Update ChromaStore to delegate indexed queries to SQLite
- Add test suite for SQLiteStore (7 tests, all passing)
:Detailed Notes:
- SQLiteStore: news_items, anomaly_types, news_anomalies tables with indexes
- Performance: get_latest/get_top_ranked O(n)→O(log n), get_stats O(n)→O(1)
- ChromaDB remains primary vector store; SQLite provides indexed metadata queries
:Testing Performed:
- python3 -m pytest tests/ -v (112 passed)
:QA Notes:
- Tests verified by Python QA Engineer subagent
:Issues Addressed:
- get_latest/get_top_ranked fetched ALL items then sorted in Python
- get_stats iterated over ALL items
- anomalies_detected stored as comma-joined string (no index)
Change-Id: I708808b6e72889869afcf16d4ac274260242007a
Artur Mukhamadiev
f4ae73bdae