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- Removed outdated validation blocking Execute Workflow Trigger workflows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/workflow-diff-engine.js

@@ -651,7 +651,7 @@ class WorkflowDiffEngine {
     validateActivateWorkflow(workflow, operation) {
         const activatableTriggers = workflow.nodes.filter(node => !node.disabled && (0, node_type_utils_1.isActivatableTrigger)(node.type));
         if (activatableTriggers.length === 0) {
-            return 'Cannot activate workflow: No activatable trigger nodes found. Workflows must have at least one enabled trigger node (webhook, schedule, email, etc.). Note: executeWorkflowTrigger cannot activate workflows as they can only be invoked by other workflows.';
+            return 'Cannot activate workflow: No activatable trigger nodes found. Workflows must have at least one enabled trigger node (webhook, schedule, executeWorkflowTrigger, etc.).';
         }
         return null;
     }