feat(agent): add read-only download.list capability

Co-Authored-By: Claude Opus 5.5 <[email protected]>

apps/server/test/e2e/e2-agent-delegate.test.ts

@@ -45,8 +45,8 @@ describe.skipIf(!hasPg)("E2 Agent 委托闭环(fake 模型 + 真实能力/授权
     return r.body.data.id as string;
   };
 
-  it("启动断言:40 个能力全部注册,并在能力目录里可见", async () => {
-    expect(e.booted.ctx.capabilities.list()).toHaveLength(40);
+  it("启动断言:41 个能力全部注册,并在能力目录里可见", async () => {
+    expect(e.booted.ctx.capabilities.list()).toHaveLength(41);
     const r = await e.api("GET", "/capabilities");
     expect(r.body.data.items.map((c: { id: string }) => c.id).sort()).toEqual(
       e.booted.ctx.capabilities