feat(admin): 分类管理（分类树增删改移 + 后台页面）

Co-Authored-By: Devin AI <158243242+devin-ai-integration[bot]@users.noreply.github.com>

api/internal/adminstore/write.go

@@ -354,19 +354,27 @@ func (s *Store) ListBrands(ctx context.Context) ([]Brand, error) {
 	return out, rows.Err()
 }
 
-// Category is a category option for the edit form.
+// Category is a category option for the edit form and the management view.
 type Category struct {
-	ID     string  `json:"id"`
-	NameZH string  `json:"name_zh"`
-	NameEN *string `json:"name_en"`
-	Path   string  `json:"path"`
-	Level  int     `json:"level"`
+	ID           string  `json:"id"`
+	NameZH       string  `json:"name_zh"`
+	NameEN       *string `json:"name_en"`
+	Path         string  `json:"path"`
+	Level        int     `json:"level"`
+	ParentID     *string `json:"parent_id"`
+	GPCBrickCode *string `json:"gpc_brick_code"`
+	ProductCount int     `json:"product_count"`
 }
 
-// ListCategories returns the full category tree.
+// ListCategories returns the full category tree (path order) with the number of
+// products directly assigned to each node.
 func (s *Store) ListCategories(ctx context.Context) ([]Category, error) {
-	rows, err := s.pool.Query(ctx,
-		"SELECT id, name_zh, name_en, path::text, level FROM category ORDER BY path")
+	rows, err := s.pool.Query(ctx, `
+SELECT c.id, c.name_zh, c.name_en, c.path::text, c.level, c.parent_id::text,
+       c.gpc_brick_code,
+       (SELECT count(*) FROM product p WHERE p.category_id = c.id) AS product_count
+FROM category c
+ORDER BY c.path`)
 	if err != nil {
 		return nil, err
 	}
@@ -374,7 +382,8 @@ func (s *Store) ListCategories(ctx context.Context) ([]Category, error) {
 	out := []Category{}
 	for rows.Next() {
 		var c Category
-		if err := rows.Scan(&c.ID, &c.NameZH, &c.NameEN, &c.Path, &c.Level); err != nil {
+		if err := rows.Scan(&c.ID, &c.NameZH, &c.NameEN, &c.Path, &c.Level,
+			&c.ParentID, &c.GPCBrickCode, &c.ProductCount); err != nil {
 			return nil, err
 		}
 		out = append(out, c)