feat(KB-044): add test coverage reporting with vitest coverage-v8

- Add @vitest/coverage-v8 to all workspace packages
- Configure vitest coverage settings in all vitest.config.ts files
- Align vitest versions across packages for consistency
- Add 'test:coverage' script to root package.json
- Verify all tests pass with coverage reporting enabled

packages/dashboard/package.json

@@ -42,10 +42,11 @@
     "@types/react": "^19.0.0",
     "@types/react-dom": "^19.0.0",
     "@vitejs/plugin-react": "^4.3.0",
+    "@vitest/coverage-v8": "^3.1.0",
     "jsdom": "^29.0.1",
     "typescript": "^5.7.0",
     "vite": "^6.0.0",
-    "vitest": "^4.1.1"
+    "vitest": "^3.1.0"
   },
   "private": true
 }