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/visual/pages.spec.js

@@ -0,0 +1,73 @@
+import { test, expect } from '@playwright/test'
+import { loginAsAdmin } from '../helpers/auth.js'
+
+const viewports = {
+  desktop: { width: 1280, height: 720 },
+  mobile: { width: 375, height: 667 },
+}
+
+const publicPages = [
+  { name: 'home', path: '/' },
+  { name: 'join', path: '/join' },
+  { name: 'events', path: '/events' },
+  { name: 'coming-soon', path: '/coming-soon' },
+]
+
+const authenticatedPages = [
+  { name: 'member-dashboard', path: '/member/dashboard' },
+  { name: 'member-profile', path: '/member/profile' },
+  { name: 'admin-members', path: '/admin/members' },
+  { name: 'admin-events-create', path: '/admin/events/create' },
+]
+
+// Wait for fonts and images to load before taking screenshots
+async function waitForStable(page) {
+  await page.waitForLoadState('networkidle')
+  // Wait for web fonts to load
+  await page.evaluate(() => document.fonts.ready)
+}
+
+test.describe('visual regression — public pages', () => {
+  for (const { name, path } of publicPages) {
+    for (const [viewportName, viewport] of Object.entries(viewports)) {
+      test(`${name} — ${viewportName}`, async ({ page }) => {
+        await page.setViewportSize(viewport)
+        await page.goto(path)
+        await waitForStable(page)
+
+        await expect(page).toHaveScreenshot(`${name}-${viewportName}.png`, {
+          maxDiffPixelRatio: 0.01,
+          mask: [
+            // Mask dynamic content like dates and counts
+            page.locator('.event-date'),
+            page.locator('.event-count'),
+            page.locator('time'),
+          ],
+        })
+      })
+    }
+  }
+})
+
+test.describe('visual regression — authenticated pages', () => {
+  test.beforeEach(async ({ page }) => {
+    await loginAsAdmin(page)
+  })
+
+  for (const { name, path } of authenticatedPages) {
+    test(`${name} — desktop`, async ({ page }) => {
+      await page.setViewportSize(viewports.desktop)
+      await page.goto(path)
+      await waitForStable(page)
+
+      await expect(page).toHaveScreenshot(`${name}-desktop.png`, {
+        maxDiffPixelRatio: 0.01,
+        mask: [
+          page.locator('.event-date'),
+          page.locator('time'),
+          page.locator('.member-since'),
+        ],
+      })
+    })
+  }
+})