Issue #3611898: Add a Remove all button to the graphical seat map's selection panel
Adds a Remove all button to the graphical seat map's "Your selection" panel.
Problem
The panel lets a visitor release seats one at a time with the per-seat remove (×) button, but there is no way to clear the whole selection in one action.
Change
- A
clearoperation on the seat-op endpoint (SeatSelectionController::act) releases every seat the session holds for the slot in a single pass, through the same booking engine and slot lock as the per-seat release. - The panel shows a full-width Remove all button below the total, only when at least one seat is held; clicking it posts
clear, resets the held seats to available on the map and empties the panel. - New JS strings go through
Drupal.t(); the button is styled with the existing panel tokens (theme-aware).
Follow-up to the graphical seat map (#3611792).