Move validation tests to plugin package

- Remove validation.test.ts from platform-node (not its responsibility)
- Remove plugin-validator devDependency from platform-node
- Validation tests already exist in plugin-validator package (52 tests)

Co-authored-by: hotlong <50353452+hotlong@users.noreply.github.com>

Author: Copilot

packages/foundation/platform-node/package.json

@@ -27,7 +27,6 @@
     "js-yaml": "^4.1.1"
   },
   "devDependencies": {
-    "@objectql/plugin-validator": "workspace:*",
     "typescript": "^5.3.0"
   }
 }