build: 初始化构建后端并集成Gin框架，开放健康检查端口

backend/cmd/main.go

@@ -0,0 +1,28 @@
+package main
+
+import (
+	"fmt"
+	"log"
+
+	"gen2d/internal/config"
+	"gen2d/internal/handler"
+
+	"github.com/gin-gonic/gin"
+)
+
+func main() {
+	cfg := config.Load()
+
+	gin.SetMode(cfg.Mode)
+
+	r := gin.New()
+	r.Use(gin.Recovery())
+
+	r.GET("/api/v1/health", handler.Health)
+
+	addr := fmt.Sprintf(":%d", cfg.Port)
+	log.Printf("gen2d backend starting on %s", addr)
+	if err := r.Run(addr); err != nil {
+		log.Fatalf("server failed: %v", err)
+	}
+}