feat(mcp): add browser_network_mock and browser_network_unmock tools

[Suhaib3100]

Summary

Fixes #38961

This PR adds two new MCP tools for mocking network responses dynamically:

New Tools

browser_network_mock

Mock a network response for a URL pattern. When a request matches the pattern, it will be fulfilled with the provided response instead of going to the network.

Parameters:

• urlPattern - URL pattern to match (glob pattern, e.g., **/api/users, https://example.com/api/**)
• response.status - HTTP status code for the mocked response (default: 200)
• response.contentType - Content-Type header (default: application/json)
• response.body - Response body as a string
• response.headers - Optional additional headers

browser_network_unmock

Remove all network mocks for a URL pattern.

Parameters:

• urlPattern - URL pattern to unmock (must match the pattern used in browser_network_mock)

Use Cases

1. AI agents can test error scenarios - Mock 500 errors, 404s, timeouts, etc.
2. Test different API responses - Mock different data without requiring a backend
3. Faster automation - No need to wait for real API calls
4. Isolated testing - Control exactly what data the application receives

Example Usage

// Set up a mock
await client.callTool({
  name: 'browser_network_mock',
  arguments: {
    urlPattern: '**/api/users',
    response: {
      status: 200,
      contentType: 'application/json',
      body: JSON.stringify([{ id: 1, name: 'John' }]),
    },
  },
});

// Remove the mock
await client.callTool({
  name: 'browser_network_unmock',
  arguments: {
    urlPattern: '**/api/users',
  },
});

Tests

Added comprehensive tests in tests/mcp/network.spec.ts:

• browser_network_mock - mock JSON API response
• browser_network_unmock - remove mock

All tests pass on chromium and chrome.