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/app/app.go

@@ -0,0 +1,68 @@
+package app
+
+import (
+	"net/http"
+
+	"github.com/fish/language/backend/internal/config"
+	"github.com/fish/language/backend/internal/handlers"
+	"github.com/fish/language/backend/internal/repository/queries"
+	"github.com/fish/language/backend/internal/services"
+	"github.com/go-chi/chi/v5"
+	"github.com/go-chi/chi/v5/middleware"
+	"github.com/jackc/pgx/v5/pgxpool"
+)
+
+// App wires all dependencies and exposes the HTTP server.
+type App struct {
+	cfg    *config.Config
+	router *chi.Mux
+	pool   *pgxpool.Pool
+}
+
+// New creates and initializes a new App.
+func New(cfg *config.Config, pool *pgxpool.Pool) *App {
+	app := &App{
+		cfg:  cfg,
+		pool: pool,
+	}
+	app.setupRouter()
+	return app
+}
+
+func (a *App) setupRouter() {
+	r := chi.NewRouter()
+	r.Use(middleware.Logger)
+	r.Use(middleware.Recoverer)
+	r.Use(middleware.RequestID)
+	r.Use(middleware.RealIP)
+	r.Use(middleware.SetHeader("Content-Type", "application/json"))
+
+	q := queries.New(a.pool)
+	categorySvc := services.NewCategoryService(q)
+	wordSvc := services.NewWordService(q)
+
+	categoryHandler := handlers.NewCategoryHandler(categorySvc)
+	wordHandler := handlers.NewWordHandler(wordSvc)
+
+	r.Route("/api/v1", func(api chi.Router) {
+		categoryHandler.Register(api)
+		wordHandler.Register(api)
+	})
+
+	r.Get("/health", func(w http.ResponseWriter, r *http.Request) {
+		w.WriteHeader(http.StatusOK)
+		_, _ = w.Write([]byte(`{"status":"ok"}`))
+	})
+
+	a.router = r
+}
+
+// Router returns the underlying chi router for testing.
+func (a *App) Router() *chi.Mux {
+	return a.router
+}
+
+// Run starts the HTTP server.
+func (a *App) Run() error {
+	return http.ListenAndServe(a.cfg.HTTPAddr, a.router)
+}