feat(tickets): suppression d'un ticket (backend + frontend)

Ajoute la suppression complète d'un ticket (#6).

Backend Rust :
- port IssueStore::delete (NotFound si absent) + event IssueDeleted{freed_sprint}
- FsIssueStore::delete : supprime .ideai/tickets/<N>/ et l'index sous lock
- use case DeleteIssue + adaptations des tests sprint/ticket_assistant au port
- commande Tauri ticket_delete + câblage events/state/lib

Frontend :
- gateway delete (ports, adapter ticket + mock, domain)
- useTicketDetail : retrait de la liste et fermeture du détail via event issueDeleted
- intégration TicketDetail + tests

Tests verts : application/issue_usecases (6), infrastructure/issue_store (7),
app-tauri --lib (56), frontend vitest (503), npm run build (exit 0).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

frontend/src/domain/index.ts

@@ -126,6 +126,19 @@ export type DomainEvent =
     }
   | { type: "issueCreated"; issueId: string; issueRef: string }
   | { type: "issueUpdated"; issueRef: string; version: number }
+  | {
+      /**
+       * A ticket was deleted (ticket #6). Mirror of the backend
+       * `DomainEventDto::IssueDeleted`. `issueRef` is the deleted `#N`;
+       * `freedSprint` is the sprint id it was released from, when any. Starts with
+       * `issue`, so {@link isTicketEvent} matches it and ticket lists refresh
+       * automatically; an open detail on the same `issueRef` closes.
+       */
+      type: "issueDeleted";
+      projectId: string;
+      issueRef: string;
+      freedSprint: string | null;
+    }
   | {
       type: "issueStatusChanged";
       issueRef: string;