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/useTicketDetail.ts

@@ -22,6 +22,12 @@ export interface TicketDetailViewModel {
   error: string | null;
   /** Set when the last write lost an optimistic-concurrency race (F3). */
   conflict: boolean;
+  /**
+   * Set once the open ticket has been deleted — by this view or any other actor
+   * (ticket #6). Driven by the `issueDeleted` domain event (single source of
+   * truth); the surface reacts by closing itself.
+   */
+  deleted: boolean;
   busy: boolean;
   /**
    * Monotonic counter bumped **only** when the ticket is (re)loaded from the
@@ -42,6 +48,12 @@ export interface TicketDetailViewModel {
   link: (targetRef: string, kind: TicketLinkKind) => Promise<boolean>;
   unlink: (targetRef: string, kind?: TicketLinkKind) => Promise<boolean>;
   assign: (agentId: string, assigned: boolean) => Promise<boolean>;
+  /**
+   * Deletes this ticket (ticket #6). Returns `true` on success. The removal from
+   * lists and the closing of this surface flow from the resulting `issueDeleted`
+   * event (see {@link TicketDetailViewModel.deleted}), not from local mutation.
+   */
+  remove: () => Promise<boolean>;
 }
 
 function describe(e: unknown): string {
@@ -69,6 +81,7 @@ export function useTicketDetail(
   const [ticket, setTicket] = useState<Ticket | null>(null);
   const [error, setError] = useState<string | null>(null);
   const [conflict, setConflict] = useState(false);
+  const [deleted, setDeleted] = useState(false);
   const [busy, setBusy] = useState(false);
   const [reloadCount, setReloadCount] = useState(0);
 
@@ -101,6 +114,12 @@ export function useTicketDetail(
     let cancelled = false;
     void system
       .onDomainEvent((event) => {
+        if (event.type === "issueDeleted" && event.issueRef === ref) {
+          // The open ticket was deleted (here or elsewhere): don't refresh (it
+          // would 404) — flag it so the surface closes (#6).
+          setDeleted(true);
+          return;
+        }
         if (isTicketEvent(event) && event.issueRef === ref) void refresh();
       })
       .then((u) => {
@@ -186,10 +205,27 @@ export function useTicketDetail(
     [run, gateway, projectId, ref],
   );
 
+  const remove: TicketDetailViewModel["remove"] = useCallback(async () => {
+    setBusy(true);
+    setError(null);
+    try {
+      await gateway.delete(projectId, ref);
+      // Closing/removal flows from the `issueDeleted` event (single source of
+      // truth) — see the `deleted` flag set in the subscription above.
+      return true;
+    } catch (e) {
+      setError(describe(e));
+      return false;
+    } finally {
+      setBusy(false);
+    }
+  }, [gateway, projectId, ref]);
+
   return {
     ticket,
     error,
     conflict,
+    deleted,
     busy,
     reloadCount,
     refresh,
@@ -198,5 +234,6 @@ export function useTicketDetail(
     link,
     unlink,
     assign,
+    remove,
   };
 }