Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

- DuckDB threads 2→1 (saves ~125MB native), memory_limit 512→256MB
- FTS rebuild interval 500→5000 (reduces frequency of expensive shadow table materialization)
- CHECKPOINT after FTS rebuild to compact WAL and free DuckDB memory
- Startup phase memory logging to diagnose where memory is consumed

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Set DuckDB memory_limit=512MB and threads=2 to prevent FTS shadow
table rebuilds from consuming all container RAM alongside V8.
Remove backfillChildTables() — was a one-time migration, child rows
are already populated during normal indexing and backfill.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>