test: run tests on MCP server inside Docker (#361)

https://github.com/microsoft/playwright-mcp/issues/346

tests/network.spec.ts

@@ -45,5 +45,5 @@ test('browser_network_requests', async ({ client, server }) => {
   await expect.poll(() => client.callTool({
     name: 'browser_network_requests',
     arguments: {},
-  })).toHaveTextContent(`[GET] http://localhost:${server.PORT}/json => [200] OK`);
+  })).toHaveTextContent(`[GET] ${`${server.PREFIX}/json`} => [200] OK`);
 });