chore: add Algolia search click tracking

[evwilkin]

closes #5006

Summary

• Adds Algolia search-insights library (CDN) to track search result clicks
• Captures queryID via XHR interception since DocSearch v2 discards it from responses
• Sends clickedObjectIDsAfterSearch events with objectID, position, and queryID
• Uses sendBeacon transport so click events survive page navigation
• Respects Do Not Track browser setting (same pattern as existing GA integration)
• 404 page search inherits tracking automatically via shared attachDocSearch()

🤖 Generated with Claude Code

Testing

To test:

1. Use the PR preview link to perform a search and click on a result. Note both the search term and the time you completed the search.
   Multiple searches can help confirm with more data points, but note that clicking on a search results takes you to the live site - use the back button from your search or reopen the preview link above to ensure any additional test searches start from the PR preview page.
2. Open the Search page at Algolia.com and ensure it's filtered to today, then refresh the page until the Last update timestamp at the top is after your search:
3. Compare the "Search" tab with the "Searches without clicks" tab to ensure your search appears on the first but not the second.

[patternfly-build]

Preview: https://pf-org--pr-5005-site.surge.sh

[jschuler]

The main thing that got flagged for me is this:

handleSelected overrides default navigation behavior (sideNavLayout.js:240-253)

The handleSelected callback ends with window.location.href = suggestion.url, re-implementing DocSearch's default navigation. If DocSearch's default behavior ever changes (e.g., SPA navigation, opening in new tab for modifier keys), this override won't pick that up. Notably, Cmd+Click / Ctrl+Click for "open in new tab" is broken — the handler unconditionally does window.location.href = ... regardless of modifier keys.

Consider checking for context === 'click' vs keyboard selection, and respecting modifier keys:

if (event.metaKey || event.ctrlKey) {
  window.open(suggestion.url, '_blank');
} else {
  window.location.href = suggestion.url;
}

[jschuler]

Tested search and the terms showed up on Algolia

[phcox]

I tested a couple of search terms and both worked as expected - no clicks showed up as such.

[phcox]

Looks good. Thanks!