feat: 实现视频分片上传与断点续传

- 后端：init/upload/status/complete 四个分片上传接口
- 后端：基于 Redis 的上传会话管理，支持断点续传
- 后端：分片 MD5 校验、幂等上传、顺序合并
- 测试：覆盖完整上传流程、断点续传、幂等性、哈希校验、未完成合并、状态查询
- 前端：Vue 3 分片上传组件，支持并发上传与进度展示

backend/internal/video/chunk_entity.go

@@ -0,0 +1,55 @@
+package video
+
+const ChunkSize = 5 << 20 // 5 MB
+
+type ChunkUploadSession struct {
+	UploadID     string `json:"upload_id"`
+	AccountID    uint   `json:"account_id"`
+	Filename     string `json:"filename"`
+	FileSize     int64  `json:"file_size"`
+	ChunkSize    int64  `json:"chunk_size"`
+	TotalChunks  int    `json:"total_chunks"`
+	FileHash     string `json:"file_hash"`
+	UploadedBits []bool `json:"uploaded_bits"`
+}
+
+func (s *ChunkUploadSession) UploadedChunks() []int {
+	var indices []int
+	for i, uploaded := range s.UploadedBits {
+		if uploaded {
+			indices = append(indices, i)
+		}
+	}
+	return indices
+}
+
+func (s *ChunkUploadSession) IsComplete() bool {
+	for _, b := range s.UploadedBits {
+		if !b {
+			return false
+		}
+	}
+	return true
+}
+
+type InitChunkUploadRequest struct {
+	Filename    string `json:"filename" binding:"required"`
+	FileSize    int64  `json:"file_size" binding:"required,min=1"`
+	ChunkSize   int64  `json:"chunk_size" binding:"required,min=1"`
+	TotalChunks int    `json:"total_chunks" binding:"required,min=1"`
+	FileHash    string `json:"file_hash" binding:"required"`
+}
+
+type UploadChunkRequest struct {
+	UploadID   string `form:"upload_id" binding:"required"`
+	ChunkIndex int    `form:"chunk_index" binding:"min=0"`
+	ChunkHash  string `form:"chunk_hash" binding:"required"`
+}
+
+type ChunkStatusRequest struct {
+	UploadID string `json:"upload_id" binding:"required"`
+}
+
+type CompleteChunkUploadRequest struct {
+	UploadID string `json:"upload_id" binding:"required"`
+}