feat(mock): 补全新功能的 mock 数据(覆盖度/覆盖图/关联/工作空间)

- data：coverage、coverageGraph(11 节点树)、assetRefsFor、WS_TREE +
  workspaceList/Read 示例文件树
- handler：/tasks/{id}/coverage · coverage-graph · asset-refs +
  /workspace/list · read 路由(写/建/删走 {ok:true} 兜底)
- api：workspaceUpload/Download 加 MOCK 守卫(裸 fetch 绕过 http 助手，
  demo 下改为 no-op/占位下载，不再网络报错)

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

web/src/lib/api.ts

@@ -144,6 +144,7 @@ export const api = {
   workspaceDelete: (path: string) =>
     del<{ ok: boolean }>(`/workspace/delete?path=${encodeURIComponent(path)}`),
   workspaceUpload: async (dir: string, files: File[]) => {
+    if (MOCK) return { uploaded: files.length };
     const fd = new FormData();
     for (const f of files) fd.append("file", f);
     const token = getToken();
@@ -156,12 +157,17 @@ export const api = {
     return r.json() as Promise<{ uploaded: number }>;
   },
   workspaceDownload: async (path: string) => {
-    const token = getToken();
-    const r = await fetch(`/api/workspace/download?path=${encodeURIComponent(path)}`, {
-      headers: { ...(token ? { Authorization: `Bearer ${token}` } : {}) },
-    });
-    if (!r.ok) throw new Error(`下载失败: ${r.status}`);
-    const blob = await r.blob();
+    let blob: Blob;
+    if (MOCK) {
+      blob = new Blob([`（demo）${path} 的下载内容示例。`], { type: "text/plain" });
+    } else {
+      const token = getToken();
+      const r = await fetch(`/api/workspace/download?path=${encodeURIComponent(path)}`, {
+        headers: { ...(token ? { Authorization: `Bearer ${token}` } : {}) },
+      });
+      if (!r.ok) throw new Error(`下载失败: ${r.status}`);
+      blob = await r.blob();
+    }
     const objUrl = URL.createObjectURL(blob);
     const a = document.createElement("a");
     a.href = objUrl;