新增语言学习后台服务

- 分类管理：支持分类的增删改查
- 单词管理：支持单词的增删改查，包含音标、释义、例句等字段
- 更新 README 项目说明

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

backend/internal/handlers/category_handler.go

@@ -0,0 +1,126 @@
+package handlers
+
+import (
+	"encoding/json"
+	"net/http"
+	"strconv"
+
+	"github.com/fish/language/backend/internal/models"
+	"github.com/fish/language/backend/internal/services"
+	"github.com/go-chi/chi/v5"
+)
+
+// CategoryHandler handles HTTP requests for categories.
+type CategoryHandler struct {
+	svc *services.CategoryService
+}
+
+// NewCategoryHandler creates a new CategoryHandler.
+func NewCategoryHandler(svc *services.CategoryService) *CategoryHandler {
+	return &CategoryHandler{svc: svc}
+}
+
+// Register mounts category routes.
+func (h *CategoryHandler) Register(r chi.Router) {
+	r.Get("/categories", h.List)
+	r.Post("/categories", h.Create)
+	r.Get("/categories/{id}", h.Get)
+	r.Put("/categories/{id}", h.Update)
+	r.Delete("/categories/{id}", h.Delete)
+}
+
+// List returns all categories.
+func (h *CategoryHandler) List(w http.ResponseWriter, r *http.Request) {
+	items, err := h.svc.List(r.Context())
+	if err != nil {
+		status, code, msg := MapError(err)
+		RespondError(w, status, code, msg)
+		return
+	}
+	RespondSuccess(w, items)
+}
+
+// Get returns a category by id.
+func (h *CategoryHandler) Get(w http.ResponseWriter, r *http.Request) {
+	id, err := parseID(r)
+	if err != nil {
+		RespondError(w, http.StatusBadRequest, 10002, "invalid id")
+		return
+	}
+	item, err := h.svc.Get(r.Context(), id)
+	if err != nil {
+		status, code, msg := MapError(err)
+		RespondError(w, status, code, msg)
+		return
+	}
+	RespondSuccess(w, item)
+}
+
+// Create creates a new category.
+func (h *CategoryHandler) Create(w http.ResponseWriter, r *http.Request) {
+	var req models.CreateCategoryRequest
+	if err := json.NewDecoder(r.Body).Decode(&req); err != nil {
+		RespondError(w, http.StatusBadRequest, 10003, "invalid request body")
+		return
+	}
+	if req.Name == "" {
+		RespondError(w, http.StatusBadRequest, 10004, "name is required")
+		return
+	}
+	item, err := h.svc.Create(r.Context(), req)
+	if err != nil {
+		status, code, msg := MapError(err)
+		RespondError(w, status, code, msg)
+		return
+	}
+	RespondJSON(w, http.StatusCreated, modelsAPIResponse{Code: 0, Message: "created", Data: item})
+}
+
+// Update updates a category.
+func (h *CategoryHandler) Update(w http.ResponseWriter, r *http.Request) {
+	id, err := parseID(r)
+	if err != nil {
+		RespondError(w, http.StatusBadRequest, 10002, "invalid id")
+		return
+	}
+	var req models.UpdateCategoryRequest
+	if err := json.NewDecoder(r.Body).Decode(&req); err != nil {
+		RespondError(w, http.StatusBadRequest, 10003, "invalid request body")
+		return
+	}
+	if req.Name == "" {
+		RespondError(w, http.StatusBadRequest, 10004, "name is required")
+		return
+	}
+	item, err := h.svc.Update(r.Context(), id, req)
+	if err != nil {
+		status, code, msg := MapError(err)
+		RespondError(w, status, code, msg)
+		return
+	}
+	RespondSuccess(w, item)
+}
+
+// Delete removes a category.
+func (h *CategoryHandler) Delete(w http.ResponseWriter, r *http.Request) {
+	id, err := parseID(r)
+	if err != nil {
+		RespondError(w, http.StatusBadRequest, 10002, "invalid id")
+		return
+	}
+	if err := h.svc.Delete(r.Context(), id); err != nil {
+		status, code, msg := MapError(err)
+		RespondError(w, status, code, msg)
+		return
+	}
+	RespondSuccess(w, nil)
+}
+
+func parseID(r *http.Request) (int32, error) {
+	idStr := chi.URLParam(r, "id")
+	id64, err := strconv.ParseInt(idStr, 10, 32)
+	if err != nil {
+		return 0, err
+	}
+	return int32(id64), nil
+}