fix: сортировка категорий в CSV-экспорте без учёта регистра

Поиск в categoryOrder не нормализовал регистр — категория "mem" не совпадала
с ключом "MEM", получала порядок 9999 и строки шли в произвольном порядке.
Заодно заменён bubble-sort на sort.SliceStable.

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

internal/services/export.go

@@ -504,29 +504,30 @@ func (s *ExportService) resolveCategories(pricelistID *uint, lotNames []string)
 	return categories
 }
 
-// defaultCategoryOrder returns a category code → display_order map built from models.DefaultCategories.
+// defaultCategoryOrder returns an uppercase category code → display_order map from models.DefaultCategories.
 func defaultCategoryOrder() map[string]int {
 	m := make(map[string]int, len(models.DefaultCategories))
 	for _, cat := range models.DefaultCategories {
-		m[cat.Code] = cat.DisplayOrder
+		m[strings.ToUpper(cat.Code)] = cat.DisplayOrder
 	}
 	return m
 }
 
+func categoryDisplayOrder(categoryOrder map[string]int, category string) (int, bool) {
+	order, ok := categoryOrder[strings.ToUpper(strings.TrimSpace(category))]
+	return order, ok
+}
+
 // sortItemsByCategory sorts items by category display order (items without category go to the end).
 func sortItemsByCategory(items []ExportItem, categoryOrder map[string]int) {
-	for i := 0; i < len(items)-1; i++ {
-		for j := i + 1; j < len(items); j++ {
-			orderI, hasI := categoryOrder[items[i].Category]
-			orderJ, hasJ := categoryOrder[items[j].Category]
-
-			if !hasI && hasJ {
-				items[i], items[j] = items[j], items[i]
-			} else if hasI && hasJ && orderI > orderJ {
-				items[i], items[j] = items[j], items[i]
-			}
+	sort.SliceStable(items, func(i, j int) bool {
+		orderI, hasI := categoryDisplayOrder(categoryOrder, items[i].Category)
+		orderJ, hasJ := categoryDisplayOrder(categoryOrder, items[j].Category)
+		if hasI && hasJ {
+			return orderI < orderJ
 		}
-	}
+		return hasI && !hasJ
+	})
 }
 
 type pricingLevels struct {