feat(sprints): interface de création et gestion des sprints (frontend)

Ticket #11 — surface UI de gestion des sprints (frontend pur).

- Nouveau composant SprintManager : création (nom optionnel), édition et
  gestion du cycle de vie d'un sprint, contrôles accessibles (pas de DnD).
- useTickets étendu aux opérations de gestion de sprint ; ports, adaptateurs
  (ticket.ts, mock/index.ts) et TicketsPanel câblés en conséquence.
- Tests Vitest associés (tickets.test.tsx).

Typecheck / vitest (497+ tests) / build verts.

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

frontend/src/adapters/ticket.ts

@@ -148,4 +148,38 @@ export class TauriTicketGateway implements TicketGateway {
       request: { projectId, ref, sprintId, expectedVersion },
     });
   }
+
+  async createSprint(projectId: string, name: string): Promise<Sprint> {
+    return invoke<Sprint>("sprint_create", {
+      request: { projectId, name },
+    });
+  }
+
+  async renameSprint(
+    projectId: string,
+    sprintId: string,
+    name: string,
+    expectedVersion: number,
+  ): Promise<Sprint> {
+    return invoke<Sprint>("sprint_rename", {
+      request: { projectId, sprintId, name, expectedVersion },
+    });
+  }
+
+  async reorderSprints(
+    projectId: string,
+    orderedIds: string[],
+  ): Promise<Sprint[]> {
+    // `sprint_reorder` returns a `SprintListDto { items }`; unwrap to the array.
+    const list = await invoke<{ items: Sprint[] }>("sprint_reorder", {
+      request: { projectId, orderedIds },
+    });
+    return list.items;
+  }
+
+  async deleteSprint(projectId: string, sprintId: string): Promise<void> {
+    await invoke<void>("sprint_delete", {
+      request: { projectId, sprintId },
+    });
+  }
 }