feat(workspace): 新增工作空间文件管理器(针对 workDir)

后端 server/workspace.go(全部在 requireAuth 之后，路径限定在 workDir):
- list/read/write/mkdir/delete/download/upload 七个端点
- wsResolve 用 Clean("/"+rel)+前缀校验防 .. 遍历；上传经 filepath.Base
  再二次校验；读文本 2MB 上限(超限/二进制仅下载)；上传 512MB 上限；
  下载文件名过滤 + filename* UTF-8 编码

前端:
- 侧边栏「工作空间」入口(/function/workspace)
- api/types：workspaceList/read/write/mkdir/delete + upload(FormData)
  + download(blob 带 token)
- page：面包屑导航 + 目录表格 + 上传/新建文件夹/刷新 + 每行下载/删除
  + 右侧 Sheet 文本编辑器(二进制/超大仅下载)

Co-Authored-By: Claude Opus 4.8 <[email protected]>

server/server.go

@@ -485,6 +485,15 @@ func (s *Server) Handler() http.Handler {
 	mux.HandleFunc("GET /api/tasks/{id}/coverage", s.taskCoverage)
 	mux.HandleFunc("GET /api/tasks/{id}/coverage-graph", s.taskCoverageGraph)
 	mux.HandleFunc("GET /api/tasks/{id}/asset-refs", s.taskAssetRefs)
+
+	// 工作空间文件管理器（针对 workDir）
+	mux.HandleFunc("GET /api/workspace/list", s.wsList)
+	mux.HandleFunc("GET /api/workspace/read", s.wsRead)
+	mux.HandleFunc("POST /api/workspace/write", s.wsWrite)
+	mux.HandleFunc("POST /api/workspace/mkdir", s.wsMkdir)
+	mux.HandleFunc("DELETE /api/workspace/delete", s.wsDelete)
+	mux.HandleFunc("GET /api/workspace/download", s.wsDownload)
+	mux.HandleFunc("POST /api/workspace/upload", s.wsUpload)
 	mux.HandleFunc("GET /api/tasks/{id}/scope", s.taskScopeList)
 	mux.HandleFunc("POST /api/tasks/{id}/control", s.control)
 	mux.HandleFunc("POST /api/active", s.setActive)