feat(web): «Deshacer» after moving, reassigning or trashing a ticket

A toast offers to undo for seven seconds (or Ctrl/⌘ Z outside a field)
by running the opposite command: the card back to its column or the
ticket to its status (the workflow may refuse it), the previous
assignee, or the ticket back from the trash. The undo itself only says
«Deshecho». On the board, from the card's assignee; on the ticket page,
status, assignee and trash, which no longer asks for confirmation.

The toast is the app's own (UndoToastComponent): pi-snack-bar cannot
tell its button from the timeout.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

libs/web/tracker/application/src/lib/notifications.ts

@@ -2,6 +2,8 @@
 export abstract class Notifications {
   abstract success(message: string): void;
   abstract error(message: string): void;
+  /** Done, offering to undo it for a few seconds: `undo` runs if asked. */
+  abstract undoable(message: string, undo: () => void): void;
 }
 
 /** Message of a failed GraphQL/HTTP call, for the user. */