feat(backend): module scaffold, config, gin router with healthz

backend/internal/api/router.go

@@ -0,0 +1,24 @@
+package api
+
+import (
+	"net/http"
+
+	"github.com/gin-gonic/gin"
+
+	"booklib/internal/config"
+)
+
+type api struct {
+	cfg *config.Config
+	// st, rdb, sc 字段在 Task 4/9 加入
+}
+
+func NewRouter(cfg *config.Config) *gin.Engine {
+	gin.SetMode(gin.ReleaseMode)
+	_ = &api{cfg: cfg} // Task 4/9 起此处为 a := &api{...}，handler 挂在 a 上
+	r := gin.New()
+	r.Use(gin.Recovery())
+	g := r.Group("/api")
+	g.GET("/healthz", func(c *gin.Context) { c.String(http.StatusOK, "ok") })
+	return r
+}