test(frontend): add vitest test suite and apply code formatting

frontend/package.json

@@ -7,11 +7,16 @@
     "dev": "vite",
     "build": "tsc && vite build",
     "preview": "vite preview",
-    "lint": "tsc --noEmit"
+    "lint": "tsc --noEmit",
+    "test": "vitest run",
+    "test:watch": "vitest"
   },
   "devDependencies": {
+    "@vitest/ui": "^4.1.10",
+    "jsdom": "^30.0.1",
     "typescript": "~6.0.2",
-    "vite": "^8.2.0"
+    "vite": "^8.2.0",
+    "vitest": "^4.1.10"
   },
   "dependencies": {
     "hls.js": "^1.6.16"