Capture network errors & add breadcrumbs ?

@niemyjski can we use [xhr onerror](https://developer.mozilla.org/en-US/docs/Web/API/XMLHttpRequestEventTarget/onerror) to capture network errors and also maybe add user breadcrumbs like click action, page load , xhr calls, console warning messages etc ?

Start by reviewing TraceKit's existing browser exception-capture entry points and determine where XMLHttpRequest errors could be observed. Define the breadcrumb events named in the issue—click actions, page loads, XHR calls, and console warnings—and verify that the completed work captures network errors and exposes those breadcrumbs alongside captured exceptions.

Written by the indexing model from the issue text.