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) {

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)

internal/services/sync/readiness.go

@@ -168,6 +168,10 @@ func ensureClientSchemaStateTable(db *gorm.DB) error {
 			"ALTER TABLE qt_client_schema_state ADD COLUMN IF NOT EXISTS competitor_pricelist_version VARCHAR(128) NULL AFTER warehouse_pricelist_version",
 			"ALTER TABLE qt_client_schema_state ADD COLUMN IF NOT EXISTS last_sync_error_code VARCHAR(128) NULL AFTER competitor_pricelist_version",
 			"ALTER TABLE qt_client_schema_state ADD COLUMN IF NOT EXISTS last_sync_error_text TEXT NULL AFTER last_sync_error_code",
+			"ALTER TABLE qt_client_schema_state ADD COLUMN IF NOT EXISTS local_pricelist_count INT NOT NULL DEFAULT 0 AFTER last_sync_error_text",
+			"ALTER TABLE qt_client_schema_state ADD COLUMN IF NOT EXISTS pricelist_items_count INT NOT NULL DEFAULT 0 AFTER local_pricelist_count",
+			"ALTER TABLE qt_client_schema_state ADD COLUMN IF NOT EXISTS components_count INT NOT NULL DEFAULT 0 AFTER pricelist_items_count",
+			"ALTER TABLE qt_client_schema_state ADD COLUMN IF NOT EXISTS db_size_bytes BIGINT NOT NULL DEFAULT 0 AFTER components_count",
 		} {
 			if err := db.Exec(stmt).Error; err != nil {
 				return fmt.Errorf("expand qt_client_schema_state: %w", err)
@@ -215,6 +219,10 @@ func (s *Service) reportClientSchemaState(mariaDB *gorm.DB, checkedAt time.Time)
 	warehouseVersion := latestPricelistVersion(s.localDB, "warehouse")
 	competitorVersion := latestPricelistVersion(s.localDB, "competitor")
 	lastSyncErrorCode, lastSyncErrorText := latestSyncErrorState(s.localDB)
+	localPricelistCount := s.localDB.CountLocalPricelists()
+	pricelistItemsCount := s.localDB.CountAllPricelistItems()
+	componentsCount := s.localDB.CountComponents()
+	dbSizeBytes := s.localDB.DBFileSizeBytes()
 	return mariaDB.Exec(`
 		INSERT INTO qt_client_schema_state (
 			username, hostname, app_version,
@@ -222,9 +230,10 @@ func (s *Service) reportClientSchemaState(mariaDB *gorm.DB, checkedAt time.Time)
 			configurations_count, projects_count,
 			estimate_pricelist_version, warehouse_pricelist_version, competitor_pricelist_version,
 			last_sync_error_code, last_sync_error_text,
+			local_pricelist_count, pricelist_items_count, components_count, db_size_bytes,
 			last_checked_at, updated_at
 		)
-		VALUES (?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?)
+		VALUES (?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?)
 		ON DUPLICATE KEY UPDATE
 			app_version = VALUES(app_version),
 			last_sync_at = VALUES(last_sync_at),
@@ -238,6 +247,10 @@ func (s *Service) reportClientSchemaState(mariaDB *gorm.DB, checkedAt time.Time)
 			competitor_pricelist_version = VALUES(competitor_pricelist_version),
 			last_sync_error_code = VALUES(last_sync_error_code),
 			last_sync_error_text = VALUES(last_sync_error_text),
+			local_pricelist_count = VALUES(local_pricelist_count),
+			pricelist_items_count = VALUES(pricelist_items_count),
+			components_count = VALUES(components_count),
+			db_size_bytes = VALUES(db_size_bytes),
 			last_checked_at = VALUES(last_checked_at),
 			updated_at = VALUES(updated_at)
 	`, username, hostname, appmeta.Version(),
@@ -245,6 +258,7 @@ func (s *Service) reportClientSchemaState(mariaDB *gorm.DB, checkedAt time.Time)
 		configurationsCount, projectsCount,
 		estimateVersion, warehouseVersion, competitorVersion,
 		lastSyncErrorCode, lastSyncErrorText,
+		localPricelistCount, pricelistItemsCount, componentsCount, dbSizeBytes,
 		checkedAt, checkedAt).Error
 }