perf: 为 /uploads 静态资源添加缓存控制

- 设置 Cache-Control: public, max-age=3600 (缓存 1 小时)
- 减少 logo、favicon 等上传文件的重复请求

backend/cmd/main.go

@@ -231,6 +231,13 @@ func startServer() {
 	r.Use(middleware.Cors())
 	r.Use(gzipMiddleware())
 
+	r.Use(func(c *gin.Context) {
+		if strings.HasPrefix(c.Request.URL.Path, "/uploads/") {
+			c.Header("Cache-Control", "public, max-age=3600")
+		}
+		c.Next()
+	})
+
 	r.Static("/uploads", "uploads")
 	router.SetupRoutes(r)
 	setupEmbeddedFrontend(r)