test(24-01): add failing test for Route 53 credential factory

- lib/types/route53.ts: camelCase interfaces for zones/records/history/audit-log/sync-result
- lib/services/route53-factory.test.ts: isRoute53Configured() + getRoute53Client() behavior
  cases — fails RED, factory module does not exist yet

lib/services/route53-factory.test.ts

@@ -0,0 +1,63 @@
+import { describe, it, expect, beforeEach, afterEach } from 'vitest';
+import { isRoute53Configured, getRoute53Client, resetRoute53Client } from './route53-factory';
+
+const ORIGINAL_ENV = { ...process.env };
+
+beforeEach(() => {
+  delete process.env.AWS_ACCESS_KEY_ID;
+  delete process.env.AWS_SECRET_ACCESS_KEY;
+  delete process.env.AWS_REGION;
+  resetRoute53Client();
+});
+
+afterEach(() => {
+  process.env = { ...ORIGINAL_ENV };
+  resetRoute53Client();
+});
+
+describe('isRoute53Configured', () => {
+  it('returns false when AWS_ACCESS_KEY_ID is unset', () => {
+    process.env.AWS_SECRET_ACCESS_KEY = 'secret1';
+    expect(isRoute53Configured()).toBe(false);
+  });
+
+  it('returns false when AWS_SECRET_ACCESS_KEY is unset', () => {
+    process.env.AWS_ACCESS_KEY_ID = 'id1';
+    expect(isRoute53Configured()).toBe(false);
+  });
+
+  it('returns false when both are set to empty strings', () => {
+    process.env.AWS_ACCESS_KEY_ID = '';
+    process.env.AWS_SECRET_ACCESS_KEY = '';
+    expect(isRoute53Configured()).toBe(false);
+  });
+
+  it('returns true when both are set to non-empty values', () => {
+    process.env.AWS_ACCESS_KEY_ID = 'id1';
+    process.env.AWS_SECRET_ACCESS_KEY = 'secret1';
+    expect(isRoute53Configured()).toBe(true);
+  });
+});
+
+describe('getRoute53Client', () => {
+  it('throws an Error mentioning AWS_ACCESS_KEY_ID when credentials are absent', () => {
+    expect(() => getRoute53Client()).toThrow(/AWS_ACCESS_KEY_ID/);
+  });
+
+  it('returns the same cached instance on a second call', () => {
+    process.env.AWS_ACCESS_KEY_ID = 'id1';
+    process.env.AWS_SECRET_ACCESS_KEY = 'secret1';
+    const first = getRoute53Client();
+    const second = getRoute53Client();
+    expect(second).toBe(first);
+  });
+
+  it('returns a different instance after resetRoute53Client()', () => {
+    process.env.AWS_ACCESS_KEY_ID = 'id1';
+    process.env.AWS_SECRET_ACCESS_KEY = 'secret1';
+    const first = getRoute53Client();
+    resetRoute53Client();
+    const second = getRoute53Client();
+    expect(second).not.toBe(first);
+  });
+});