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/adminhandler/handler.go

@@ -77,6 +77,9 @@ func (h *Handler) Router() http.Handler {
 			r.Post("/api/products/{id}/barcodes/{barcodeID}/primary", h.SetPrimaryBarcode)
 			r.Get("/api/brands", h.ListBrands)
 			r.Get("/api/categories", h.ListCategories)
+			r.Post("/api/categories", h.CreateCategory)
+			r.Put("/api/categories/{id}", h.UpdateCategory)
+			r.Delete("/api/categories/{id}", h.DeleteCategory)
 
 			r.Get("/api/submissions", h.ListSubmissions)
 			r.Get("/api/submissions/{id}", h.GetSubmission)
@@ -328,6 +331,74 @@ func (h *Handler) ListCategories(w http.ResponseWriter, r *http.Request) {
 	writeJSON(w, http.StatusOK, map[string]any{"items": items})
 }
 
+// CreateCategory adds a category node.
+func (h *Handler) CreateCategory(w http.ResponseWriter, r *http.Request) {
+	var in adminstore.CategoryInput
+	if err := json.NewDecoder(r.Body).Decode(&in); err != nil {
+		writeError(w, http.StatusBadRequest, "bad_request", "invalid body")
+		return
+	}
+	if strings.TrimSpace(in.NameZH) == "" {
+		writeError(w, http.StatusBadRequest, "bad_request", "分类名称不能为空")
+		return
+	}
+	c, err := h.store.CreateCategory(r.Context(), auth.UserFrom(r.Context()), in)
+	if h.handleCategoryErr(w, err) {
+		return
+	}
+	writeJSON(w, http.StatusCreated, c)
+}
+
+// UpdateCategory renames and/or moves a category node.
+func (h *Handler) UpdateCategory(w http.ResponseWriter, r *http.Request) {
+	var in adminstore.CategoryInput
+	if err := json.NewDecoder(r.Body).Decode(&in); err != nil {
+		writeError(w, http.StatusBadRequest, "bad_request", "invalid body")
+		return
+	}
+	if strings.TrimSpace(in.NameZH) == "" {
+		writeError(w, http.StatusBadRequest, "bad_request", "分类名称不能为空")
+		return
+	}
+	c, err := h.store.UpdateCategory(r.Context(), chi.URLParam(r, "id"), auth.UserFrom(r.Context()), in)
+	if h.handleCategoryErr(w, err) {
+		return
+	}
+	writeJSON(w, http.StatusOK, c)
+}
+
+// DeleteCategory removes a leaf category that no product uses.
+func (h *Handler) DeleteCategory(w http.ResponseWriter, r *http.Request) {
+	err := h.store.DeleteCategory(r.Context(), chi.URLParam(r, "id"), auth.UserFrom(r.Context()))
+	if h.handleCategoryErr(w, err) {
+		return
+	}
+	writeJSON(w, http.StatusOK, map[string]string{"status": "deleted"})
+}
+
+// handleCategoryErr maps category-specific errors to client statuses, falling
+// back to handleErr otherwise.
+func (h *Handler) handleCategoryErr(w http.ResponseWriter, err error) bool {
+	if err == nil {
+		return false
+	}
+	switch {
+	case errors.Is(err, adminstore.ErrDuplicatePath):
+		writeError(w, http.StatusConflict, "duplicate_path", "该分类路径已存在，请换一个英文标识(slug)")
+		return true
+	case errors.Is(err, adminstore.ErrCategoryHasChildren):
+		writeError(w, http.StatusConflict, "has_children", "该分类存在子分类，请先删除或移动其子分类")
+		return true
+	case errors.Is(err, adminstore.ErrCategoryInUse):
+		writeError(w, http.StatusConflict, "in_use", "仍有商品归属于该分类，请先改归其它分类")
+		return true
+	case errors.Is(err, adminstore.ErrInvalidParent):
+		writeError(w, http.StatusBadRequest, "invalid_parent", "上级分类无效（不存在或不能移动到自身/子级下）")
+		return true
+	}
+	return h.handleErr(w, err)
+}
+
 // ---------- submissions ----------
 
 // CreateSubmission accepts an anonymous public contribution into the queue.