Fix plugin architecture: import Validator from plugin package

- Revert core re-exports to avoid circular dependency
- Update test to import from @objectql/plugin-validator
- Add plugin-validator as devDependency to platform-node

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

Author: Copilot

packages/foundation/core/src/index.ts

@@ -30,7 +30,3 @@ export * from './query';
 // Export utilities
 export * from './util';
 export * from './ai-agent';
-
-// Re-export plugin classes for backward compatibility
-export { Validator, ValidatorPlugin } from '@objectql/plugin-validator';
-export { FormulaEngine, FormulaPlugin } from '@objectql/plugin-formula';

packages/foundation/platform-node/package.json

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

packages/foundation/platform-node/test/validation.test.ts

@@ -6,7 +6,7 @@
  * LICENSE file in the root directory of this source tree.
  */
 
-import { Validator } from '@objectql/core';
+import { Validator } from '@objectql/plugin-validator';
 import {
     ValidationContext,
     AnyValidationRule,