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/fixtures.js

@@ -0,0 +1,23 @@
+import { test as base } from '@playwright/test'
+import { loginAsAdmin, loginAsMember } from './auth.js'
+
+/**
+ * Extended test fixtures with pre-authenticated pages.
+ */
+export const test = base.extend({
+  adminPage: async ({ page }, use) => {
+    await loginAsAdmin(page)
+    await use(page)
+  },
+  memberPage: async ({ browser }, use) => {
+    // Uses a default test member — tests needing a specific member
+    // should use loginAsMember directly
+    const context = await browser.newContext()
+    const page = await context.newPage()
+    await loginAsMember(page, 'test-admin@ghostguild.dev')
+    await use(page)
+    await context.close()
+  },
+})
+
+export { expect } from '@playwright/test'