fix: correct error code access path in integration tests

The validation errors have the code inside details.code, not at the top level.
Updated all integration tests to access e.details?.code || e.code instead of e.code.

This fixes all 23 failing integration tests:
- AI Agent validation tests
- AI Tool validation tests
- Chat Trigger validation tests
- E2E validation tests
- LLM Chain validation tests

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

tests/integration/ai-validation/e2e-validation.test.ts

@@ -210,7 +210,7 @@ describe('Integration: End-to-End AI Workflow Validation', () => {
     expect(validationData.errors!.length).toBeGreaterThan(3);
 
     // Verify specific errors are detected
-    const errorCodes = validationData.errors!.map(e => e.code);
+    const errorCodes = validationData.errors!.map(e => e.details?.code || e.code);
 
     expect(errorCodes).toContain('MISSING_LANGUAGE_MODEL'); // AI Agent
     expect(errorCodes).toContain('MISSING_PROMPT_TEXT'); // AI Agent