feat: 增加共享 Agent Browser 调试能力

需求：在 AI 编程会话中让用户与 Agent 共享同一浏览器页面，并查看控制台与网络信息。

实现：新增沙箱浏览器内核、Host API/渲染器面板、OpenCode 工具接入及安全边界测试。

tests/unit/host-events.test.ts

@@ -44,6 +44,23 @@ describe('host-events', () => {
     expect(cleanupSpy).toHaveBeenCalledTimes(1);
   });
 
+  it.each(['agent-browser:show', 'agent-browser:state'])(
+    'maps %s to the preload IPC bridge',
+    async (eventName) => {
+      const onMock = vi.mocked(window.electron.ipcRenderer.on);
+      const cleanupSpy = vi.fn();
+      onMock.mockReturnValue(cleanupSpy);
+
+      const { subscribeHostEvent } = await import('@/lib/host-events');
+      const unsubscribe = subscribeHostEvent(eventName, vi.fn());
+
+      expect(onMock).toHaveBeenCalledWith(eventName, expect.any(Function));
+      expect(createHostEventSourceMock).not.toHaveBeenCalled();
+      unsubscribe();
+      expect(cleanupSpy).toHaveBeenCalledTimes(1);
+    },
+  );
+
   it('does not use SSE fallback by default for unknown events', async () => {
     const warnSpy = vi.spyOn(console, 'warn').mockImplementation(() => {});
     const { subscribeHostEvent } = await import('@/lib/host-events');