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>

internal/services/quote.go

@@ -388,13 +388,14 @@ func (s *QuoteService) lookupPricesByPricelistID(pricelistID uint, lotNames []st
 		}
 	}
 
-	// Fallback path (usually offline): local per-lot lookup.
+	// Fallback path (usually offline): batch local lookup (single query via index).
 	if s.localDB != nil {
-		for _, lotName := range missing {
-			price, found := s.lookupPriceByPricelistID(pricelistID, lotName)
-			if found && price > 0 {
-				result[lotName] = price
-				loaded[lotName] = price
+		if localPL, err := s.localDB.GetLocalPricelistByServerID(pricelistID); err == nil {
+			if batchPrices, err := s.localDB.GetLocalPricesForLots(localPL.ID, missing); err == nil {
+				for lotName, price := range batchPrices {
+					result[lotName] = price
+					loaded[lotName] = price
+				}
 			}
 		}
 		s.updateCache(pricelistID, missing, loaded)