feat: Add analyze_heapsnapshot_contexts MCP tool

[dinfuehr]

Add a MCP tool for detecting dead context variables in a heap snapshot. It can detect for example cases like this:

function setupUserSession(userId) {
  const largeBuffer = new ArrayBuffer(10 * 1024 * 1024); // 10MB
  let isOnline = true;

  // Force largeBuffer into context.
  fetch('/api/sync').then(() => {
    processData(largeBuffer);
  });

  // Long-lived event listener uses isOnline in same
  // context object and keeps alive largeBuffer.
  window.addEventListener('online', () => {
    updateStatus(userId, isOnline);
  });
}

[dinfuehr]

Thanks a lot for the review! I've updated the PR, so PTAL again

[Lightning00Blade]

Still LGTM!