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/adapters/mock/index.ts

@@ -2012,6 +2012,22 @@ export class MockTicketGateway implements TicketGateway {
     return structuredClone(ticket);
   }
 
+  async delete(projectId: string, ref: string): Promise<void> {
+    // NotFound if absent (mirrors the backend `AppError::NotFound`).
+    const ticket = this.require(projectId, ref);
+    const freedSprint = ticket.sprintId ?? null;
+    this.projectTickets(projectId).delete(ref);
+    this.projectCarnets(projectId).delete(ref);
+    // Releasing the ticket updates its former sprint's count.
+    if (freedSprint) this.recountSprints(projectId);
+    this.system?.emit({
+      type: "issueDeleted",
+      projectId,
+      issueRef: ref,
+      freedSprint,
+    });
+  }
+
   async readCarnet(projectId: string, ref: string): Promise<TicketCarnet> {
     const ticket = this.require(projectId, ref);
     return {

frontend/src/adapters/ticket.ts

@@ -73,6 +73,15 @@ export class TauriTicketGateway implements TicketGateway {
     });
   }
 
+  async delete(projectId: string, ref: string): Promise<void> {
+    // `ticket_delete` takes the shared `{ request }` envelope like every other
+    // ticket command; a missing ref surfaces as a `NOT_FOUND` GatewayError from
+    // the backend, propagated as-is.
+    await invoke<void>("ticket_delete", {
+      request: { projectId, ref },
+    });
+  }
+
   async readCarnet(projectId: string, ref: string): Promise<TicketCarnet> {
     return invoke<TicketCarnet>("ticket_read_carnet", {
       request: { projectId, ref },