feat: 编辑器增加「重置」和「丢弃预览版」按钮，支持回退预览版快照

par-api/src/main/java/com/par/api/controller/AdminController.java

@@ -462,6 +462,15 @@ public class AdminController {
         return ApiResponse.success(result);
     }
 
+    /** 丢弃预览版快照（删除所有 draft），站点配置回退到正式版 */
+    @PostMapping("/sites/{siteId}/discard-draft")
+    public ApiResponse<Map<String, Object>> discardDraft(@PathVariable("siteId") String siteId,
+                                                          HttpServletRequest request) {
+        checkAdmin(request);
+        int deleted = snapshotService.discardDraft(siteId);
+        return ApiResponse.success(Map.of("siteId", siteId, "deleted", deleted));
+    }
+
     @GetMapping("/sites")
     public ApiResponse<List<com.par.core.dto.SiteDTO>> listAllSites(HttpServletRequest request) {
         checkAdmin(request);