GUI: add confirm dialogs to close tourney and other buttons with critical actions

* [ ] Critical actions must have a confirm dialog (see example with disconnect, concede);
* [ ] Confirm dialog for critical action must have default button on cancel, not ok (so random enter/space keys must not able to confirm it);
* [ ] Critical action buttons must be unfocusable (not so good solution) or there are must be another buttons to take a focus by default (good solution;

Start by locating the GUI handlers for closing a tournament and the existing disconnect and concede confirmation dialogs. Audit other critical-action buttons for confirmation, safe default-button behavior, and keyboard focus handling; done means every critical action follows these safeguards.

Written by the indexing model from the issue text.