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

frontend/package-lock.json

@@ -9,6 +9,7 @@
       "version": "0.0.0",
       "dependencies": {
         "pinia": "^3.0.4",
+        "spark-md5": "^3.0.2",
         "vue": "^3.5.24",
         "vue-router": "^4.6.4"
       },
@@ -1173,6 +1174,12 @@
         "node": ">=0.10.0"
       }
     },
+    "node_modules/spark-md5": {
+      "version": "3.0.2",
+      "resolved": "https://registry.npmmirror.com/spark-md5/-/spark-md5-3.0.2.tgz",
+      "integrity": "sha512-wcFzz9cDfbuqe0FZzfi2or1sgyIrsDwmPwfZC4hiNidPdPINjeUwNfv5kldczoEAcjl9Y1L3SM7Uz2PUEQzxQw==",
+      "license": "(WTFPL OR MIT)"
+    },
     "node_modules/speakingurl": {
       "version": "14.0.1",
       "resolved": "https://registry.npmmirror.com/speakingurl/-/speakingurl-14.0.1.tgz",