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/features/tickets/TicketDetail.tsx

@@ -104,6 +104,14 @@ export function TicketDetail({
   const [copied, setCopied] = useState(false);
   // Confirmation shown when the user tries to close with unsaved changes.
   const [confirmClose, setConfirmClose] = useState(false);
+  // Confirmation shown before deleting the ticket (#6).
+  const [confirmDelete, setConfirmDelete] = useState(false);
+
+  // The ticket was deleted (by this view or another actor): close the surface.
+  // The removal from lists flows from the same `issueDeleted` event (#6).
+  useEffect(() => {
+    if (vm.deleted) onClose();
+  }, [vm.deleted, onClose]);
 
   const reloadCount = vm.reloadCount;
   const seededReload = useRef(-1);
@@ -205,6 +213,16 @@ export function TicketDetail({
           >
             {copied ? "Copied" : "Delegation context"}
           </Button>
+          <Button
+            size="sm"
+            variant="ghost"
+            disabled={!t || vm.busy}
+            onClick={() => setConfirmDelete(true)}
+            className="text-danger hover:text-danger"
+            title="Supprimer définitivement ce ticket"
+          >
+            Supprimer
+          </Button>
           <Button size="sm" variant="ghost" onClick={requestClose}>
             Close
           </Button>
@@ -559,6 +577,52 @@ export function TicketDetail({
           </div>
         </div>
       )}
+
+      {/* ── Delete confirmation (#6) ── */}
+      {confirmDelete && (
+        <div
+          role="dialog"
+          aria-modal="true"
+          aria-label="confirmer la suppression"
+          className="fixed inset-0 z-[60] flex items-center justify-center bg-black/55 p-4"
+        >
+          <div className="w-full max-w-sm rounded-lg border border-border bg-surface p-5 shadow-xl">
+            <h4 className="text-sm font-semibold text-content">
+              Supprimer le ticket
+            </h4>
+            <p className="mt-2 text-sm text-muted">
+              Supprimer définitivement le ticket&nbsp;{ticketRef}&nbsp;? Cette
+              action est irréversible.
+            </p>
+            <div className="mt-4 flex flex-wrap items-center justify-end gap-2">
+              <Button
+                size="sm"
+                variant="ghost"
+                aria-label="cancel delete"
+                disabled={vm.busy}
+                onClick={() => setConfirmDelete(false)}
+              >
+                Annuler
+              </Button>
+              <Button
+                size="sm"
+                variant="danger"
+                aria-label="confirm delete"
+                loading={vm.busy}
+                disabled={vm.busy}
+                onClick={async () => {
+                  const ok = await vm.remove();
+                  // On success the surface closes via the `issueDeleted` event
+                  // (the `deleted` flag → onClose effect); just drop the dialog.
+                  if (ok) setConfirmDelete(false);
+                }}
+              >
+                Supprimer
+              </Button>
+            </div>
+          </div>
+        </div>
+      )}
     </div>
   );
 }