fix(frontend): harden the streaming ui and extract copy and constants

frontend/package.json

@@ -8,6 +8,7 @@
     "build": "vue-tsc -b && vite build",
     "preview": "vite preview",
     "lint": "eslint src",
+    "test": "vitest run",
     "format": "prettier --write src",
     "typecheck": "vue-tsc --noEmit -p tsconfig.app.json"
   },
@@ -22,10 +23,12 @@
     "@vue/tsconfig": "^0.9.1",
     "eslint": "^10.8.1",
     "eslint-plugin-vue": "^10.10.0",
+    "happy-dom": "^20.11.2",
     "jiti": "^2.7.0",
     "prettier": "^3.9.6",
     "typescript": "~6.0.2",
     "vite": "^8.2.0",
+    "vitest": "^4.1.10",
     "vue-tsc": "^3.3.8"
   }
 }