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/mock/index.ts

@@ -36,6 +36,7 @@ import type {
   ResumableAgent,
   Skill,
   SkillScope,
+  Sprint,
   Template,
   TerminalSession,
   Ticket,
@@ -1813,12 +1814,14 @@ export class MockTicketGateway implements TicketGateway {
   private tickets = new Map<string, Map<string, Ticket>>();
   private carnets = new Map<string, Map<string, string>>();
   private counters = new Map<string, number>();
+  private sprints = new Map<string, Map<string, Sprint>>();
 
   constructor(private readonly system?: MockSystemGateway) {}
 
   /** Seeds a ticket for deterministic tests; returns the stored clone. */
   _seedTicket(projectId: string, ticket: Ticket): Ticket {
     const stored = structuredClone(ticket);
+    if (stored.sprintId === undefined) stored.sprintId = null;
     this.projectTickets(projectId).set(stored.ref, stored);
     this.counters.set(
       projectId,
@@ -1827,6 +1830,41 @@ export class MockTicketGateway implements TicketGateway {
     return structuredClone(stored);
   }
 
+  /** Seeds a sprint for deterministic tests; returns the stored clone. */
+  _seedSprint(
+    projectId: string,
+    sprint: Pick<Sprint, "id" | "order" | "name"> &
+      Partial<Pick<Sprint, "status" | "ticketCount" | "version">>,
+  ): Sprint {
+    const stored: Sprint = {
+      status: "planned",
+      ticketCount: 0,
+      version: 1,
+      ...sprint,
+    };
+    this.projectSprints(projectId).set(stored.id, stored);
+    return structuredClone(stored);
+  }
+
+  private projectSprints(projectId: string): Map<string, Sprint> {
+    let map = this.sprints.get(projectId);
+    if (!map) {
+      map = new Map();
+      this.sprints.set(projectId, map);
+    }
+    return map;
+  }
+
+  /** Recomputes `ticketCount` for every sprint from the current tickets. */
+  private recountSprints(projectId: string): void {
+    const sprints = this.projectSprints(projectId);
+    const counts = new Map<string, number>();
+    for (const t of this.projectTickets(projectId).values()) {
+      if (t.sprintId) counts.set(t.sprintId, (counts.get(t.sprintId) ?? 0) + 1);
+    }
+    for (const s of sprints.values()) s.ticketCount = counts.get(s.id) ?? 0;
+  }
+
   private projectTickets(projectId: string): Map<string, Ticket> {
     let map = this.tickets.get(projectId);
     if (!map) {
@@ -1874,6 +1912,7 @@ export class MockTicketGateway implements TicketGateway {
       description: input.description ?? "",
       status: input.status ?? "open",
       priority: input.priority ?? "medium",
+      sprintId: null,
       links: [],
       assignedAgentIds: [...(input.assignedAgentIds ?? [])],
       createdBy: { kind: "user" },
@@ -1930,6 +1969,7 @@ export class MockTicketGateway implements TicketGateway {
         title: t.title,
         status: t.status,
         priority: t.priority,
+        sprintId: t.sprintId ?? null,
         assignedAgentIds: [...t.assignedAgentIds],
         updatedAt: t.updatedAt,
       })),
@@ -2066,6 +2106,41 @@ export class MockTicketGateway implements TicketGateway {
     });
     return structuredClone(ticket);
   }
+
+  async listSprints(projectId: string): Promise<Sprint[]> {
+    this.recountSprints(projectId);
+    return [...this.projectSprints(projectId).values()]
+      .sort((a, b) => a.order - b.order)
+      .map((s) => structuredClone(s));
+  }
+
+  async setTicketSprint(
+    projectId: string,
+    ref: string,
+    sprintId: string | null,
+    expectedVersion: number,
+  ): Promise<Ticket> {
+    const ticket = this.require(projectId, ref);
+    this.guard(ticket, expectedVersion);
+    if (sprintId !== null && !this.projectSprints(projectId).has(sprintId)) {
+      throw {
+        code: "NOT_FOUND",
+        message: `sprint ${sprintId} not found`,
+      } as GatewayError;
+    }
+    const from = ticket.sprintId ?? null;
+    ticket.sprintId = sprintId;
+    this.bump(ticket);
+    this.recountSprints(projectId);
+    this.system?.emit({
+      type: "issueSprintChanged",
+      issueRef: ref,
+      from,
+      to: sprintId,
+      version: ticket.version,
+    });
+    return structuredClone(ticket);
+  }
 }
 
 function mostRestrictive(