feat(video): 添加视频封面功能支持

- 在表单数据结构中新增 videoCoverUrl 字段
- 为视频封面字段添加必填验证规则
- 更新初始表单数据以包含视频封面URL字段

src/views/system/physical/videoContent/index.vue

@@ -263,7 +263,8 @@ const initFormData: VideoContentForm = {
   status: 'up',
   createdAt: undefined,
   updatedAt: undefined,
-  ossId: undefined
+  ossId: undefined,
+  videoCoverUrl: undefined
 };
 const data = reactive<PageData<VideoContentForm, VideoContentQuery>>({
   form: { ...initFormData },
@@ -289,6 +290,7 @@ const data = reactive<PageData<VideoContentForm, VideoContentQuery>>({
     previewDurationSeconds: [{ required: true, message: '免费试看时长，单位：秒不能为空', trigger: 'blur' }],
     subscriptionValidHours: [{ required: true, message: '订阅后可观看的有效期，单位：小时不能为空', trigger: 'blur' }],
     ossVideoUrl: [{ required: true, message: '视频文件在阿里云OSS上的完整访问URL不能为空', trigger: 'blur' }],
+    videoCoverUrl: [{ required: true, message: '视频封面不能为空', trigger: 'blur' }],
     status: [{ required: true, message: '视频状态：up=已上架不能为空', trigger: 'change' }],
     categoryTagId: [{ required: true, message: '不能为空', trigger: 'blur' }]
   }