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/web/tracker/domain/src/lib/ports/gateways.ts

@@ -115,6 +115,11 @@ export abstract class IssuesGateway {
     parentId: string | null,
   ): Observable<CommandResult>;
   abstract epics(projectId: string): Observable<Epic[]>;
+  /** To the trash (whoever opened it, or a manager). */
+  abstract trash(issueId: string): Observable<CommandResult>;
+  abstract restore(issueId: string): Observable<CommandResult>;
+  /** The project's tickets in the trash, newest first. */
+  abstract trashed(projectId: string): Observable<IssueSummary[]>;
   /** The same change on several tickets; each may refuse on its own. */
   abstract bulkUpdate(
     issueIds: string[],