perf: enable WAL mode, batch price lookup, add DB diagnostics to schema_state
- Set PRAGMA journal_mode=WAL + synchronous=NORMAL on SQLite open;
eliminates read blocking during background pricelist sync writes
- Replace N+1 per-lot price loop in QuoteService local fallback with
GetLocalPricesForLots batch query (120 queries → 3 per price-levels call)
- Add CountAllPricelistItems, CountComponents, DBFileSizeBytes to LocalDB
- Report local_pricelist_count, pricelist_items_count, components_count,
db_size_bytes in qt_client_schema_state for performance diagnostics
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
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