feat(sprints): surface frontend du modèle de sprints

Ticket #10 — volet frontend des sprints.

- Domaine et ports frontend étendus au modèle de sprints (domain/index.ts,
  ports/index.ts).
- Adaptateurs : ticket.ts et mock/index.ts câblent les opérations sprints.
- UI tickets : useTickets + TicketsPanel exposent le rattachement/gestion des
  sprints, avec tests Vitest associés.

Typecheck / vitest / build verts.

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

frontend/src/adapters/ticket.ts

@@ -14,6 +14,7 @@ import { invoke } from "@tauri-apps/api/core";
 
 import type {
   GatewayError,
+  Sprint,
   Ticket,
   TicketCarnet,
   TicketLinkKind,
@@ -122,4 +123,29 @@ export class TauriTicketGateway implements TicketGateway {
       request: { projectId, ref, agentId, assigned, expectedVersion },
     });
   }
+
+  async listSprints(projectId: string): Promise<Sprint[]> {
+    // `sprint_list` returns a `SprintListDto { items }`; unwrap to the array.
+    const list = await invoke<{ items: Sprint[] }>("sprint_list", {
+      request: { projectId },
+    });
+    return list.items;
+  }
+
+  async setTicketSprint(
+    projectId: string,
+    ref: string,
+    sprintId: string | null,
+    expectedVersion: number,
+  ): Promise<Ticket> {
+    // Two backend commands: assign to a sprint, or unassign (clear membership).
+    if (sprintId === null) {
+      return invoke<Ticket>("ticket_unassign_sprint", {
+        request: { projectId, ref, expectedVersion },
+      });
+    }
+    return invoke<Ticket>("ticket_assign_sprint", {
+      request: { projectId, ref, sprintId, expectedVersion },
+    });
+  }
 }