test: strengthen user-path coverage and CI gates (#5308)

webui/package.json

@@ -8,6 +8,7 @@
     "build": "tsc -p tsconfig.build.json && vite build",
     "preview": "vite preview",
     "test": "vitest run",
+    "test:coverage": "vitest run --coverage",
     "test:watch": "vitest",
     "lint": "cd .. && eslint --config webui/eslint.config.js webui/src \"nanobot/channels/*/webui/**/*.{ts,tsx}\" --max-warnings 0"
   },
@@ -47,6 +48,7 @@
     "@types/react-dom": "^18.3.5",
     "@types/react-syntax-highlighter": "^15.5.13",
     "@vitejs/plugin-react": "^4.3.4",
+    "@vitest/coverage-v8": "2.1.9",
     "autoprefixer": "^10.4.20",
     "eslint": "^10.4.0",
     "eslint-plugin-react-hooks": "^7.1.1",