feat: a trash for tickets

Deleting a ticket now sends it to the trash, for whoever opened it or an
admin: it disappears from boards, searches and statistics, cannot change,
and comes back from the ticket page or the trash page for 30 days. After
that it is deleted for good with the usual cascade.

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

libs/api/tracker/presenters/src/lib/http/dto/responses.dto.ts

@@ -309,6 +309,13 @@ export class IssueDto {
   })
   rank!: string;
   @ApiProperty({ type: [ChecklistItemDto] }) checklist!: ChecklistItemDto[];
+  @ApiProperty({
+    type: String,
+    nullable: true,
+    format: 'date-time',
+    description: 'In the trash since then; null when it is not',
+  })
+  trashedAt!: string | null;
   @ApiProperty({
     type: [DevLinkDto],
     description: 'Commits, branches and pull requests that mention it',