fix: validation bugs — If/Switch version check, Set false positive, bare expressions (#675, #676, #677) (#678)

- #675: Wire `validateConditionNodeStructure` into `WorkflowValidator` with
  version-conditional checks (If v2.2+ requires options, v2.0-2.1 validates
  operators, v1.x skipped; Switch v3.2+ requires options)
- #676: Fix `validateSet` to check `assignments.assignments` (v3+) alongside
  `config.values` (v1/v2), eliminating false positive warnings
- #677: Add anchored heuristic pre-pass in `ExpressionValidator` detecting bare
  `$json`, `$node`, `$input`, `$execution`, `$workflow`, `$prevNode`, `$env`,
  `$now`, `$today`, `$itemIndex`, `$runIndex` references missing `={{ }}`

25 new tests across 3 test files.

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

Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

tests/unit/services/expression-validator.test.ts

@@ -105,6 +105,78 @@ describe('ExpressionValidator', () => {
     });
   });
 
+  describe('bare expression detection', () => {
+    it('should warn on bare $json.name', () => {
+      const params = { value: '$json.name' };
+      const result = ExpressionValidator.validateNodeExpressions(params, defaultContext);
+      expect(result.warnings.some(w => w.includes('unwrapped expression'))).toBe(true);
+    });
+
+    it('should warn on bare $node["Webhook"].json', () => {
+      const params = { value: '$node["Webhook"].json' };
+      const result = ExpressionValidator.validateNodeExpressions(params, defaultContext);
+      expect(result.warnings.some(w => w.includes('unwrapped expression'))).toBe(true);
+    });
+
+    it('should warn on bare $now', () => {
+      const params = { value: '$now' };
+      const result = ExpressionValidator.validateNodeExpressions(params, defaultContext);
+      expect(result.warnings.some(w => w.includes('unwrapped expression'))).toBe(true);
+    });
+
+    it('should warn on bare $execution.id', () => {
+      const params = { value: '$execution.id' };
+      const result = ExpressionValidator.validateNodeExpressions(params, defaultContext);
+      expect(result.warnings.some(w => w.includes('unwrapped expression'))).toBe(true);
+    });
+
+    it('should warn on bare $env.API_KEY', () => {
+      const params = { value: '$env.API_KEY' };
+      const result = ExpressionValidator.validateNodeExpressions(params, defaultContext);
+      expect(result.warnings.some(w => w.includes('unwrapped expression'))).toBe(true);
+    });
+
+    it('should warn on bare $input.item.json.field', () => {
+      const params = { value: '$input.item.json.field' };
+      const result = ExpressionValidator.validateNodeExpressions(params, defaultContext);
+      expect(result.warnings.some(w => w.includes('unwrapped expression'))).toBe(true);
+    });
+
+    it('should NOT warn on properly wrapped ={{ $json.name }}', () => {
+      const params = { value: '={{ $json.name }}' };
+      const result = ExpressionValidator.validateNodeExpressions(params, defaultContext);
+      expect(result.warnings.some(w => w.includes('unwrapped expression'))).toBe(false);
+    });
+
+    it('should NOT warn on properly wrapped {{ $json.name }}', () => {
+      const params = { value: '{{ $json.name }}' };
+      const result = ExpressionValidator.validateNodeExpressions(params, defaultContext);
+      expect(result.warnings.some(w => w.includes('unwrapped expression'))).toBe(false);
+    });
+
+    it('should NOT warn when $json appears mid-string', () => {
+      const params = { value: 'The $json data is ready' };
+      const result = ExpressionValidator.validateNodeExpressions(params, defaultContext);
+      expect(result.warnings.some(w => w.includes('unwrapped expression'))).toBe(false);
+    });
+
+    it('should NOT warn on plain text', () => {
+      const params = { value: 'Hello World' };
+      const result = ExpressionValidator.validateNodeExpressions(params, defaultContext);
+      expect(result.warnings.some(w => w.includes('unwrapped expression'))).toBe(false);
+    });
+
+    it('should detect bare expression in nested structure', () => {
+      const params = {
+        assignments: {
+          assignments: [{ value: '$json.name' }]
+        }
+      };
+      const result = ExpressionValidator.validateNodeExpressions(params, defaultContext);
+      expect(result.warnings.some(w => w.includes('unwrapped expression'))).toBe(true);
+    });
+  });
+
   describe('edge cases', () => {
     it('should handle empty expressions', () => {
       const result = ExpressionValidator.validateExpression('{{ }}', defaultContext);