feat(features): contract suites for all repository interfaces

Each repository interface now has a contract suite under
src/__contracts__/. Both Mock and Payload implementations run the
same suite, eliminating mock-vs-real drift. Payload impls back the
contract with an in-memory stub via vi.mock('payload') + a small
buildPayloadStub helper.

Spec: §5.2, §6.4

packages/navigation/src/infrastructure/repositories/mock-header.repository.test.ts

@@ -0,0 +1,7 @@
+import { describe } from "vitest";
+import { MockHeaderRepository } from "@/infrastructure/repositories/mock-header.repository";
+import { headerRepositoryContract } from "@/__contracts__/header-repository.contract";
+
+describe("MockHeaderRepository", () => {
+  headerRepositoryContract.run(() => new MockHeaderRepository());
+});

packages/navigation/src/infrastructure/repositories/payload-header.repository.test.ts

@@ -0,0 +1,44 @@
+import { describe, vi } from "vitest";
+import { PayloadHeaderRepository } from "@/infrastructure/repositories/payload-header.repository";
+import { headerRepositoryContract } from "@/__contracts__/header-repository.contract";
+import { stubPayloadConfig } from "@repo/core-testing/payload/stub-config";
+
+// ---------------------------------------------------------------------------
+// In-memory Payload stub for header (Global)
+// ---------------------------------------------------------------------------
+
+function buildHeaderStub() {
+  const globalData = {
+    logo: null,
+    items: [
+      { label: "Home", href: "/", external: false },
+      { label: "Blog", href: "/blog", external: false },
+      { label: "About", href: "/about", external: false },
+    ],
+  };
+
+  return {
+    findGlobal: vi.fn(async () => {
+      return { ...globalData };
+    }),
+  };
+}
+
+vi.mock("payload", () => ({
+  getPayload: vi.fn(),
+}));
+
+// ---------------------------------------------------------------------------
+// Contract suite
+// ---------------------------------------------------------------------------
+
+describe("PayloadHeaderRepository", () => {
+  describe("contract", () => {
+    headerRepositoryContract.run(async () => {
+      const stub = buildHeaderStub();
+      const { getPayload } = await import("payload");
+      (getPayload as ReturnType<typeof vi.fn>).mockResolvedValue(stub);
+      return new PayloadHeaderRepository(stubPayloadConfig);
+    });
+  });
+});