feat: 腾讯云 COS 迁移至火山引擎 TOS 对象存储

签名算法从 COS HMAC-SHA1 改为 TOS V4 HMAC-SHA256，
更新前后端上传凭证字段、配置项、备份脚本和文档。

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

frontend/hooks/useOSSUpload.ts

@@ -57,19 +57,19 @@ export function useOSSUpload(fileType: string = 'general'): UseOSSUploadReturn {
       setProgress(10)
       const policy = await api.getUploadPolicy(fileType)
 
-      // 2. 构建 COS 直传 FormData
+      // 2. 构建 TOS 直传 FormData
       const fileKey = `${policy.dir}${Date.now()}_${file.name}`
       const formData = new FormData()
       formData.append('key', fileKey)
-      formData.append('q-sign-algorithm', policy.q_sign_algorithm)
-      formData.append('q-ak', policy.q_ak)
-      formData.append('q-key-time', policy.q_key_time)
-      formData.append('q-signature', policy.q_signature)
+      formData.append('x-tos-algorithm', policy.x_tos_algorithm)
+      formData.append('x-tos-credential', policy.x_tos_credential)
+      formData.append('x-tos-date', policy.x_tos_date)
+      formData.append('x-tos-signature', policy.x_tos_signature)
       formData.append('policy', policy.policy)
       formData.append('success_action_status', '200')
       formData.append('file', file)
 
-      // 3. 上传到 COS
+      // 3. 上传到 TOS
       setProgress(30)
       const xhr = new XMLHttpRequest()
       await new Promise<void>((resolve, reject) => {