外观设置改为半屏布局；背景图仅保存后生效，并支持媒体库选用。

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

backend/handler/upload.go

@@ -7,7 +7,6 @@ import (
 	"strconv"
 
 	"github.com/freefire/jiang13-bbs/middleware"
-	"github.com/freefire/jiang13-bbs/realtime"
 	"github.com/freefire/jiang13-bbs/service"
 	"github.com/gin-gonic/gin"
 )
@@ -167,10 +166,9 @@ func (h *Handlers) DeleteAttachment(c *gin.Context) {
 	c.JSON(http.StatusOK, gin.H{"ok": true})
 }
 
-// UploadBackground 超管上传站点背景图（JPEG/PNG/WebP），并立即绑定前台或后台
+// UploadBackground 超管上传站点背景图（JPEG/PNG/WebP），只落盘返回 URL，不写站点设置
 func (h *Handlers) UploadBackground(c *gin.Context) {
-	surface, ok := service.NormalizeBgSurface(c.PostForm("surface"))
-	if !ok {
+	if _, ok := service.NormalizeBgSurface(c.PostForm("surface")); !ok {
 		c.JSON(http.StatusBadRequest, gin.H{"error": "请指定前台或后台（surface=site|admin）"})
 		return
 	}
@@ -209,26 +207,36 @@ func (h *Handlers) UploadBackground(c *gin.Context) {
 		c.JSON(http.StatusBadRequest, gin.H{"error": err.Error()})
 		return
 	}
+	c.JSON(http.StatusOK, gin.H{"url": url})
+}
 
-	if err := h.applyBgURL(surface, url); err != nil {
-		writeBgSettingError(c, err)
+type backgroundFromMediaRequest struct {
+	AttachmentID uint   `json:"attachment_id"`
+	Surface      string `json:"surface"`
+}
+
+// UploadBackgroundFromMedia 把本人媒体库图片复制进 backgrounds，不写站点设置
+func (h *Handlers) UploadBackgroundFromMedia(c *gin.Context) {
+	var req backgroundFromMediaRequest
+	if err := c.ShouldBindJSON(&req); err != nil || req.AttachmentID == 0 {
+		c.JSON(http.StatusBadRequest, gin.H{"error": "请选择媒体库中的图片"})
 		return
 	}
-
-	saved, err := h.Setting.Public()
+	if _, ok := service.NormalizeBgSurface(req.Surface); !ok {
+		c.JSON(http.StatusBadRequest, gin.H{"error": "请指定前台或后台（surface=site|admin）"})
+		return
+	}
+	claims := middleware.CurrentUser(c)
+	if claims == nil {
+		c.JSON(http.StatusUnauthorized, gin.H{"error": "请先登录"})
+		return
+	}
+	url, err := h.Upload.CopyBackgroundFromMedia(claims.ID, req.AttachmentID)
 	if err != nil {
-		c.JSON(http.StatusInternalServerError, gin.H{"error": "获取站点设置失败"})
+		c.JSON(http.StatusBadRequest, gin.H{"error": err.Error()})
 		return
 	}
-	payload := settingsPayload(saved)
-	h.Hub.BroadcastAll(realtime.Envelope{
-		Type: realtime.EventSettingsChanged,
-		Data: payload,
-	})
-	out := settingsPayload(saved)
-	out["ok"] = true
-	out["url"] = url
-	c.JSON(http.StatusOK, out)
+	c.JSON(http.StatusOK, gin.H{"url": url})
 }
 
 // UploadBrand 超管上传 Logo / Favicon，只落盘返回 URL，不写站点设置