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.

.github/workflows/test.yml

@@ -0,0 +1,94 @@
+name: Test
+
+on:
+  push:
+    branches: [main]
+  pull_request:
+    branches: [main]
+
+jobs:
+  vitest:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+      - uses: actions/setup-node@v4
+        with:
+          node-version: 22
+          cache: npm
+      - run: npm ci
+      - run: npm run test:run
+
+  playwright:
+    runs-on: ubuntu-latest
+    needs: vitest
+    services:
+      mongo:
+        image: mongo:7
+        ports:
+          - 27017:27017
+    env:
+      MONGODB_URI: mongodb://localhost:27017/ghostguild-test
+      JWT_SECRET: ci-test-jwt-secret
+      NUXT_PUBLIC_COMING_SOON: 'false'
+      NODE_ENV: development
+    steps:
+      - uses: actions/checkout@v4
+      - uses: actions/setup-node@v4
+        with:
+          node-version: 22
+          cache: npm
+      - run: npm ci
+      - run: npx playwright install --with-deps chromium
+      - run: npm run build
+      - name: Start server
+        run: node .output/server/index.mjs &
+        env:
+          PORT: 3000
+      - name: Wait for server
+        run: npx wait-on http://localhost:3000 --timeout 30000
+      - run: npx playwright test --ignore-snapshots
+      - uses: actions/upload-artifact@v4
+        if: failure()
+        with:
+          name: playwright-report
+          path: |
+            playwright-report/
+            e2e/test-results/
+          retention-days: 7
+
+  visual:
+    runs-on: ubuntu-latest
+    needs: vitest
+    continue-on-error: true
+    services:
+      mongo:
+        image: mongo:7
+        ports:
+          - 27017:27017
+    env:
+      MONGODB_URI: mongodb://localhost:27017/ghostguild-test
+      JWT_SECRET: ci-test-jwt-secret
+      NUXT_PUBLIC_COMING_SOON: 'false'
+      NODE_ENV: development
+    steps:
+      - uses: actions/checkout@v4
+      - uses: actions/setup-node@v4
+        with:
+          node-version: 22
+          cache: npm
+      - run: npm ci
+      - run: npx playwright install --with-deps chromium
+      - run: npm run build
+      - name: Start server
+        run: node .output/server/index.mjs &
+        env:
+          PORT: 3000
+      - name: Wait for server
+        run: npx wait-on http://localhost:3000 --timeout 30000
+      - run: npx playwright test e2e/visual/
+      - uses: actions/upload-artifact@v4
+        if: failure()
+        with:
+          name: visual-diffs
+          path: e2e/test-results/
+          retention-days: 7