feat: Brief附件/项目平台/规则AI解析/消息中心修复 + 项目创建通知

- Brief 支持代理商附件上传 (迁移 007)
- 项目新增 platform 字段 (迁移 008)，前端创建/展示平台信息
- 修复 AI 规则解析：处理中文引号导致 JSON 解析失败的问题
- 修复消息中心崩溃：补全后端消息类型映射 + fallback 保护
- 项目创建时自动发送消息通知
- .gitignore 排除 backend/data/ 数据库文件

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

frontend/hooks/useOSSUpload.ts

@@ -53,47 +53,12 @@ export function useOSSUpload(fileType: string = 'general'): UseOSSUploadReturn {
         return result
       }
 
-      // 1. 获取上传凭证
-      setProgress(10)
-      const policy = await api.getUploadPolicy(fileType)
-
-      // 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('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 TOS
-      setProgress(30)
-      const xhr = new XMLHttpRequest()
-      await new Promise<void>((resolve, reject) => {
-        xhr.upload.onprogress = (e) => {
-          if (e.lengthComputable) {
-            setProgress(30 + Math.round((e.loaded / e.total) * 50))
-          }
-        }
-        xhr.onload = () => {
-          if (xhr.status >= 200 && xhr.status < 300) {
-            resolve()
-          } else {
-            reject(new Error(`上传失败: ${xhr.status}`))
-          }
-        }
-        xhr.onerror = () => reject(new Error('网络错误'))
-        xhr.open('POST', policy.host)
-        xhr.send(formData)
+      // 后端代理上传：文件 → 后端 → TOS，避免浏览器 CORS/代理问题
+      setProgress(5)
+      const result = await api.proxyUpload(file, fileType, (pct) => {
+        setProgress(5 + Math.round(pct * 0.9))
       })
 
-      // 4. 回调通知后端
-      setProgress(90)
-      const result = await api.fileUploaded(fileKey, file.name, file.size, fileType)
-
       setProgress(100)
       setIsUploading(false)
       return {