fix: Add helpful error messages for 'changes' vs 'updates' parameter (Issue #392)

Fixed cryptic "Cannot read properties of undefined (reading 'name')" error when
users mistakenly use 'changes' instead of 'updates' in updateNode operations.

Changes:
- Added early validation in validateUpdateNode() to detect common parameter mistake
- Provides clear, educational error messages with examples
- Fixed outdated documentation example in VS_CODE_PROJECT_SETUP.md
- Added comprehensive test coverage (2 test cases)

Error Messages:
- Before: "Diff engine error: Cannot read properties of undefined (reading 'name')"
- After: "Invalid parameter 'changes'. The updateNode operation requires 'updates'
  (not 'changes'). Example: {type: "updateNode", nodeId: "abc", updates: {...}}"

Testing:
- Test coverage: 85% confidence (production ready)
- n8n-mcp-tester: All 3 test cases passed
- Code review: Approved with minor optional suggestions

Impact:
- AI agents now receive actionable error messages
- Self-correction enabled through clear examples
- Zero breaking changes (backward compatible)
- Follows existing patterns from Issue #249

Files Modified:
- src/services/workflow-diff-engine.ts (10 lines added)
- docs/VS_CODE_PROJECT_SETUP.md (1 line fixed)
- tests/unit/services/workflow-diff-engine.test.ts (2 tests added)
- CHANGELOG.md (comprehensive entry)
- package.json (version bump to 2.22.12)

Fixes #392

Conceived by Romuald Członkowski - www.aiadvisors.pl/en

tests/unit/services/workflow-diff-engine.test.ts

@@ -380,10 +380,52 @@ describe('WorkflowDiffEngine', () => {
       };
 
       const result = await diffEngine.applyDiff(baseWorkflow, request);
-      
+
       expect(result.success).toBe(false);
       expect(result.errors![0].message).toContain('Node not found');
     });
+
+    it('should provide helpful error when using "changes" instead of "updates" (Issue #392)', async () => {
+      // Simulate the common mistake of using "changes" instead of "updates"
+      const operation: any = {
+        type: 'updateNode',
+        nodeId: 'http-1',
+        changes: {  // Wrong property name
+          'parameters.url': 'https://example.com'
+        }
+      };
+
+      const request: WorkflowDiffRequest = {
+        id: 'test-workflow',
+        operations: [operation]
+      };
+
+      const result = await diffEngine.applyDiff(baseWorkflow, request);
+
+      expect(result.success).toBe(false);
+      expect(result.errors![0].message).toContain('Invalid parameter \'changes\'');
+      expect(result.errors![0].message).toContain('requires \'updates\'');
+      expect(result.errors![0].message).toContain('Example:');
+    });
+
+    it('should provide helpful error when "updates" parameter is missing', async () => {
+      const operation: any = {
+        type: 'updateNode',
+        nodeId: 'http-1'
+        // Missing "updates" property
+      };
+
+      const request: WorkflowDiffRequest = {
+        id: 'test-workflow',
+        operations: [operation]
+      };
+
+      const result = await diffEngine.applyDiff(baseWorkflow, request);
+
+      expect(result.success).toBe(false);
+      expect(result.errors![0].message).toContain('Missing required parameter \'updates\'');
+      expect(result.errors![0].message).toContain('Example:');
+    });
   });
 
   describe('MoveNode Operation', () => {