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/auth/src/__contracts__/users-repository.contract.ts

@@ -1,6 +1,6 @@
 import { it, expect, beforeEach } from "vitest";
 import { defineContractSuite } from "@repo/core-testing/contract";
-import type { IUsersRepository } from "../application/repositories/users-repository.interface.js";
+import type { IUsersRepository } from "../application/repositories/users.repository.interface.js";
 import { userFactory } from "../__factories__/user.factory.js";
 
 export const usersRepositoryContract =