Removes the standalone toolbar severity <select> and instead builds a
second <thead> row in JS with a text input (debounced 300 ms) per
column and a <select> for icon-only columns (severity_icon, status).
All active column filters apply together (AND logic). Adds data-col
attributes to <th> elements so JS can identify columns by name.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
