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/cli/package.json

@@ -60,6 +60,7 @@
     "@kb/dashboard": "workspace:*",
     "@kb/engine": "workspace:*",
     "@sinclair/typebox": "^0.34.0",
+    "@vitest/coverage-v8": "^3.1.0",
     "tsup": "^8.5.1",
     "tsx": "^4.19.0",
     "typescript": "^5.7.0",