feat: 交付官方 Docker 运行时，外观改背景图并下线自定义 CSS/JS

站点/后台分轨背景与用户列表排序一并落地；生产 CORS 改走 SITE_URL，健康检查带版本号。

Co-authored-by: Cursor <cursoragent@cursor.com>

backend/handler/health.go

@@ -4,14 +4,23 @@ import (
 	"net/http"
 
 	"github.com/freefire/jiang13-bbs/model"
+	"github.com/freefire/jiang13-bbs/version"
 	"github.com/gin-gonic/gin"
 )
 
-// Health 健康检查
+// Health 健康检查（官方运行时 Docker HEALTHCHECK 与反代 /health）
 func (h *Handlers) Health(c *gin.Context) {
 	if err := model.PingDB(); err != nil {
-		c.JSON(http.StatusServiceUnavailable, gin.H{"status": "error", "error": err.Error()})
+		c.JSON(http.StatusServiceUnavailable, gin.H{
+			"status":  "error",
+			"error":   err.Error(),
+			"version": version.Version,
+		})
 		return
 	}
-	c.JSON(http.StatusOK, gin.H{"status": "ok"})
+	c.JSON(http.StatusOK, gin.H{
+		"status":  "ok",
+		"version": version.Version,
+		"commit":  version.Commit,
+	})
 }