Slim leading checkbox on every row, tinted-row state when selected.
Bulk-action toolbar appears only when selection is non-empty: select
all (visible), clear, export selected (via exportTranscriptsToDir),
delete selected (single confirm). Esc clears selection. Cmd/Ctrl+A
selects all visible when focus is inside the list and not in a text
input. Stop-propagation on the checkbox keeps the click off the
row-expand toggle.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>