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/word_handler.go

@@ -0,0 +1,136 @@
+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"
+)
+
+// WordHandler handles HTTP requests for words.
+type WordHandler struct {
+	svc *services.WordService
+}
+
+// NewWordHandler creates a new WordHandler.
+func NewWordHandler(svc *services.WordService) *WordHandler {
+	return &WordHandler{svc: svc}
+}
+
+// Register mounts word routes.
+func (h *WordHandler) Register(r chi.Router) {
+	r.Get("/words", h.List)
+	r.Post("/words", h.Create)
+	r.Get("/words/{id}", h.Get)
+	r.Put("/words/{id}", h.Update)
+	r.Delete("/words/{id}", h.Delete)
+}
+
+// List returns a paginated list of words.
+func (h *WordHandler) List(w http.ResponseWriter, r *http.Request) {
+	req := models.ListWordsRequest{}
+	if v := r.URL.Query().Get("category_id"); v != "" {
+		if id64, err := strconv.ParseInt(v, 10, 32); err == nil {
+			id := int32(id64)
+			req.CategoryID = &id
+		}
+	}
+	req.Keyword = r.URL.Query().Get("keyword")
+	if v := r.URL.Query().Get("page"); v != "" {
+		if page, err := strconv.ParseInt(v, 10, 32); err == nil {
+			req.Page = int32(page)
+		}
+	}
+	if v := r.URL.Query().Get("page_size"); v != "" {
+		if ps, err := strconv.ParseInt(v, 10, 32); err == nil {
+			req.PageSize = int32(ps)
+		}
+	}
+
+	resp, err := h.svc.List(r.Context(), req)
+	if err != nil {
+		status, code, msg := MapError(err)
+		RespondError(w, status, code, msg)
+		return
+	}
+	RespondSuccess(w, resp)
+}
+
+// Get returns a word by id.
+func (h *WordHandler) 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 word.
+func (h *WordHandler) Create(w http.ResponseWriter, r *http.Request) {
+	var req models.CreateWordRequest
+	if err := json.NewDecoder(r.Body).Decode(&req); err != nil {
+		RespondError(w, http.StatusBadRequest, 10003, "invalid request body")
+		return
+	}
+	if req.Word == "" || req.Translation == "" || req.CategoryID == 0 {
+		RespondError(w, http.StatusBadRequest, 10004, "word, translation and category_id are 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 word.
+func (h *WordHandler) 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.UpdateWordRequest
+	if err := json.NewDecoder(r.Body).Decode(&req); err != nil {
+		RespondError(w, http.StatusBadRequest, 10003, "invalid request body")
+		return
+	}
+	if req.Word == "" || req.Translation == "" || req.CategoryID == 0 {
+		RespondError(w, http.StatusBadRequest, 10004, "word, translation and category_id are 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 word.
+func (h *WordHandler) 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)
+}