refactor(features): rename mock/payload/interface files per Lazar pattern

Convention now: <name>.repository.{ts,mock.ts,interface.ts}.
Renames .mock prefix to .mock suffix; drops .payload prefix from real
impls (canonical name = real impl); dot-separates the .repository
qualifier in interface filenames. Class names follow suit:
PayloadXRepository → XRepository; Mock* unchanged.

Refactor log: §1, §3
Spec: §9.1

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

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

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