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.

e2e/helpers/auth.js

@@ -0,0 +1,21 @@
+/**
+ * Login helpers using dev endpoints.
+ * These set real httpOnly JWT cookies so all middleware works naturally.
+ */
+
+/**
+ * Login as admin via the dev test-login endpoint.
+ * Creates a test admin user if none exists.
+ */
+export async function loginAsAdmin(page) {
+  await page.goto('/api/dev/test-login')
+  await page.waitForURL('**/admin**')
+}
+
+/**
+ * Login as a specific member by email via the dev member-login endpoint.
+ */
+export async function loginAsMember(page, email) {
+  await page.goto(`/api/dev/member-login?email=${encodeURIComponent(email)}`)
+  await page.waitForURL('**/member/**')
+}