feat: Set up JavaScript testing framework (Vitest + Playwright)

- Created package.json with Vitest and Playwright dependencies
- Configured vitest.config.js with happy-dom environment
- Configured playwright.config.js with Chromium browser
- Created test directory structure (tests/frontend/unit and e2e)
- Added setup.test.js with 10 Vitest validation tests
- Added setup.spec.js with 6 Playwright E2E validation tests
- Created FRONTEND_SETUP.md with Node.js installation guide
- Updated instructions.md marking task complete

Note: Requires Node.js installation before running tests

package.json

@@ -0,0 +1,27 @@
+{
+  "name": "aniworld-web",
+  "version": "1.0.0",
+  "description": "Aniworld Anime Download Manager - Web Frontend",
+  "type": "module",
+  "scripts": {
+    "test": "vitest run",
+    "test:watch": "vitest",
+    "test:ui": "vitest --ui",
+    "test:coverage": "vitest run --coverage",
+    "test:e2e": "playwright test",
+    "test:e2e:ui": "playwright test --ui",
+    "test:e2e:headed": "playwright test --headed",
+    "test:e2e:debug": "playwright test --debug",
+    "playwright:install": "playwright install --with-deps chromium"
+  },
+  "devDependencies": {
+    "@playwright/test": "^1.41.0",
+    "@vitest/coverage-v8": "^1.2.0",
+    "@vitest/ui": "^1.2.0",
+    "happy-dom": "^13.3.5",
+    "vitest": "^1.2.0"
+  },
+  "engines": {
+    "node": ">=18.0.0"
+  }
+}