test(web): add middleware + i18n + messages test suites (GOO-60)

Cover frontend middleware auth/locale logic, i18n config/routing/request/navigation,
and vi/en message parity — 91 new tests across 6 files.

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

apps/web/i18n/__tests__/config.spec.ts

@@ -0,0 +1,49 @@
+import { describe, expect, it } from 'vitest';
+import { locales, defaultLocale } from '../config';
+import type { Locale } from '../config';
+
+describe('i18n/config', () => {
+  describe('locales', () => {
+    it('exports an array of supported locales', () => {
+      expect(Array.isArray(locales)).toBe(true);
+      expect(locales.length).toBeGreaterThanOrEqual(2);
+    });
+
+    it('includes Vietnamese (vi) as a supported locale', () => {
+      expect(locales).toContain('vi');
+    });
+
+    it('includes English (en) as a supported locale', () => {
+      expect(locales).toContain('en');
+    });
+
+    it('only contains vi and en', () => {
+      expect([...locales]).toEqual(['vi', 'en']);
+    });
+
+    it('is a readonly tuple', () => {
+      // TypeScript const assertion — runtime check that it behaves as expected
+      const copy = [...locales];
+      expect(copy).toEqual(['vi', 'en']);
+    });
+  });
+
+  describe('defaultLocale', () => {
+    it('is set to Vietnamese (vi)', () => {
+      expect(defaultLocale).toBe('vi');
+    });
+
+    it('is one of the supported locales', () => {
+      expect(locales).toContain(defaultLocale);
+    });
+  });
+
+  describe('Locale type', () => {
+    it('accepts valid locale values', () => {
+      const vi: Locale = 'vi';
+      const en: Locale = 'en';
+      expect(vi).toBe('vi');
+      expect(en).toBe('en');
+    });
+  });
+});