feat: add _cnd conditional operator support and n8n 2.0+ executeWorkflowTrigger fix

Added:
- Support for all 12 _cnd operators in displayOptions validation (eq, not, gte, lte, gt, lt, between, startsWith, endsWith, includes, regex, exists)
- Version-based visibility checking with @version in config
- 42 new unit tests for _cnd operators

Fixed:
- n8n 2.0+ breaking change: executeWorkflowTrigger now recognized as activatable trigger
- Removed outdated validation blocking Execute Workflow Trigger workflows

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

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

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

dist/services/n8n-validation.js

@@ -217,12 +217,9 @@ function validateWorkflowStructure(workflow) {
     }
     if (workflow.active === true && workflow.nodes && workflow.nodes.length > 0) {
         const activatableTriggers = workflow.nodes.filter(node => !node.disabled && (0, node_type_utils_1.isActivatableTrigger)(node.type));
-        const executeWorkflowTriggers = workflow.nodes.filter(node => !node.disabled && node.type.toLowerCase().includes('executeworkflow'));
-        if (activatableTriggers.length === 0 && executeWorkflowTriggers.length > 0) {
-            const triggerNames = executeWorkflowTriggers.map(n => n.name).join(', ');
-            errors.push(`Cannot activate workflow with only Execute Workflow Trigger nodes (${triggerNames}). ` +
-                'Execute Workflow Trigger can only be invoked by other workflows, not activated. ' +
-                'Either deactivate the workflow or add a webhook/schedule/polling trigger.');
+        if (activatableTriggers.length === 0) {
+            errors.push('Cannot activate workflow: No activatable trigger nodes found. ' +
+                'Workflows must have at least one enabled trigger node (webhook, schedule, executeWorkflowTrigger, etc.).');
         }
     }
     if (workflow.nodes && workflow.connections) {