feat: dialogs open and close smoothly, the backdrop fading with them

internal/server/web/static/terminal.js

@@ -732,8 +732,8 @@
     // then runs once the dialog is shut and focus is back where it was, so
     // what it focuses stays focused.
     function close(then) {
-      d.classList.add('closing');
-      setTimeout(() => { d.classList.remove('closing'); d.close(); if (then) then(); }, 160);
+      d.close();
+      if (then) then();
     }
     d.addEventListener('cancel', ev => { ev.preventDefault(); close(); });
     d.addEventListener('click', ev => { if (ev.target === d) close(); });