Fix Query Stats tab stuck on loading spinner

[antarr]

Summary

The Query Stats tab was stuck showing its loading spinner indefinitely. Root cause: the sort dropdown and refresh button in _tab_query_stats.html.erb were commented out (in commit 79a17f7, when sortable column headers were introduced as a replacement), but the JavaScript that reads el('qstats-sort').value and attaches listeners to #qstats-refresh / #qstats-sort was left in place. When the tab loaded, loadQueryStats() showed the spinner, then threw TypeError: Cannot read properties of null (reading 'value') on the dropdown read — the fetch was never issued and the spinner stayed up forever.

The Dashboard tab's "Top 5 expensive queries" widget was unaffected because it uses its own ajaxGet(ROUTES.query_stats, { sort: 'total_time', limit: 5 }, ...) call that doesn't touch the removed DOM elements.

Fix

• Remove the commented-out <!--div>...</div--> block from _tab_query_stats.html.erb
• Remove the var sort = el('qstats-sort').value; line from loadQueryStats() in index.html.erb
• Hardcode sort: 'total_time' in the ajaxGet call (matches the controller's default)
• Remove the two addEventListener calls for the non-existent elements

Client-side sortable column headers (added in 79a17f7) continue to provide sort UX after the data loads.

Context

Originally committed as 37dbf8e on the feature/mysql-genius-core-phase-1a branch (PR #5) where it was a pre-existing-bug drive-by fix uncovered during testing. Cherry-picked here as a standalone PR so the fix can land on main independently of the larger Phase 1a refactor. When PR #5 merges, git's 3-way merge will detect the identical change already on main and merge cleanly without conflict or duplication.

Test Plan

• Click the Query Stats tab in a host app that uses mysql_genius
• Verify the table loads with the top 50 queries by total time
• Verify column headers are clickable for client-side sorting
• Verify no JavaScript errors in the browser console