feat: add testing infrastructure — Vitest, Playwright, CI, git hooks

Add comprehensive testing covering 420 unit/handler tests across 24 Vitest
files, 9 Playwright E2E specs, accessibility scans, and visual regression.
Includes GitHub Actions CI, Husky pre-push hook, and TESTING.md docs.

tests/server/api/auth-login.test.js

@@ -1,7 +1,7 @@
 import { describe, it, expect, vi, beforeEach } from 'vitest'
 
 vi.mock('../../../server/models/member.js', () => ({
-  default: { findOne: vi.fn() }
+  default: { findOne: vi.fn(), findByIdAndUpdate: vi.fn() }
 }))
 
 vi.mock('../../../server/utils/mongoose.js', () => ({