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/localdb/localdb.go

@@ -116,6 +116,14 @@ func New(dbPath string) (*LocalDB, error) {
 		return nil, fmt.Errorf("opening sqlite database: %w", err)
 	}
 
+	// Enable WAL mode so background sync writes never block UI reads.
+	if err := db.Exec("PRAGMA journal_mode=WAL").Error; err != nil {
+		slog.Warn("failed to enable WAL mode", "error", err)
+	}
+	if err := db.Exec("PRAGMA synchronous=NORMAL").Error; err != nil {
+		slog.Warn("failed to set synchronous=NORMAL", "error", err)
+	}
+
 	if err := ensureLocalProjectsTable(db); err != nil {
 		return nil, fmt.Errorf("ensure local_projects table: %w", err)
 	}
@@ -1152,6 +1160,29 @@ func (l *LocalDB) CountLocalPricelists() int64 {
 	return count
 }
 
+// CountAllPricelistItems returns total rows across all local_pricelist_items.
+func (l *LocalDB) CountAllPricelistItems() int64 {
+	var count int64
+	l.db.Model(&LocalPricelistItem{}).Count(&count)
+	return count
+}
+
+// CountComponents returns the number of rows in local_components.
+func (l *LocalDB) CountComponents() int64 {
+	var count int64
+	l.db.Model(&LocalComponent{}).Count(&count)
+	return count
+}
+
+// DBFileSizeBytes returns the size of the SQLite database file in bytes.
+func (l *LocalDB) DBFileSizeBytes() int64 {
+	info, err := os.Stat(l.path)
+	if err != nil {
+		return 0
+	}
+	return info.Size()
+}
+
 // GetLatestLocalPricelist returns the most recently synced pricelist
 func (l *LocalDB) GetLatestLocalPricelist() (*LocalPricelist, error) {
 	var pricelist LocalPricelist
@@ -1319,6 +1350,32 @@ func (l *LocalDB) GetLocalPriceForLot(pricelistID uint, lotName string) (float64
 	return item.Price, nil
 }
 
+// GetLocalPricesForLots returns prices for multiple lots from a local pricelist in a single query.
+// Uses the composite index (pricelist_id, lot_name). Missing lots are omitted from the result.
+func (l *LocalDB) GetLocalPricesForLots(pricelistID uint, lotNames []string) (map[string]float64, error) {
+	result := make(map[string]float64, len(lotNames))
+	if len(lotNames) == 0 {
+		return result, nil
+	}
+	type row struct {
+		LotName string  `gorm:"column:lot_name"`
+		Price   float64 `gorm:"column:price"`
+	}
+	var rows []row
+	if err := l.db.Model(&LocalPricelistItem{}).
+		Select("lot_name, price").
+		Where("pricelist_id = ? AND lot_name IN ?", pricelistID, lotNames).
+		Find(&rows).Error; err != nil {
+		return nil, err
+	}
+	for _, r := range rows {
+		if r.Price > 0 {
+			result[r.LotName] = r.Price
+		}
+	}
+	return result, nil
+}
+
 // GetLocalLotCategoriesByServerPricelistID returns lot_category for each lot_name from a local pricelist resolved by server ID.
 // Missing lots are not included in the map; caller is responsible for strict validation.
 func (l *LocalDB) GetLocalLotCategoriesByServerPricelistID(serverPricelistID uint, lotNames []string) (map[string]string, error) {