fix: recognize all trigger node types including executeWorkflowTrigger (#351) (#352)

This fix addresses issue #351 where Execute Workflow Trigger and other
trigger nodes were incorrectly treated as regular nodes, causing
"disconnected node" errors during partial workflow updates.

## Changes

**1. Created Shared Trigger Detection Utilities**
- src/utils/node-type-utils.ts:
  - isTriggerNode(): Recognizes ALL trigger types using flexible pattern matching
  - isActivatableTrigger(): Returns false for executeWorkflowTrigger (not activatable)
  - getTriggerTypeDescription(): Human-readable trigger descriptions

**2. Updated Workflow Validation**
- src/services/n8n-validation.ts:
  - Replaced hardcoded webhookTypes Set with isTriggerNode() function
  - Added validation preventing activation of workflows with only executeWorkflowTrigger
  - Now recognizes 200+ trigger types across n8n packages

**3. Updated Workflow Validator**
- src/services/workflow-validator.ts:
  - Replaced inline trigger detection with shared isTriggerNode() function
  - Ensures consistency across all validation code paths

**4. Comprehensive Tests**
- tests/unit/utils/node-type-utils.test.ts:
  - Added 30+ tests for trigger detection functions
  - Validates all trigger types are recognized correctly
  - Confirms executeWorkflowTrigger is trigger but not activatable

## Impact

Before:
- Execute Workflow Trigger flagged as disconnected node
- Schedule/email/polling triggers also rejected
- Users forced to keep unnecessary webhook triggers

After:
- ALL trigger types recognized (executeWorkflowTrigger, scheduleTrigger, etc.)
- No disconnected node errors for triggers
- Clear error when activating workflow with only executeWorkflowTrigger
- Future-proof (new triggers automatically supported)

## Testing

- Build: ✅ Passes
- Typecheck: ✅ Passes
- Unit tests: ✅ All pass
- Validation test: ✅ Trigger detection working correctly

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

src/services/n8n-validation.ts

@@ -1,6 +1,7 @@
 import { z } from 'zod';
 import { WorkflowNode, WorkflowConnection, Workflow } from '../types/n8n-api';
-import { isNonExecutableNode, isTriggerNode } from '../utils/node-classification';
+import { isTriggerNode, isActivatableTrigger } from '../utils/node-type-utils';
+import { isNonExecutableNode } from '../utils/node-classification';
 
 // Zod schemas for n8n API validation
 
@@ -257,10 +258,10 @@ export function validateWorkflowStructure(workflow: Partial<Workflow>): string[]
         }
 
         const isConnected = connectedNodes.has(node.name);
-        const isTrigger = isTriggerNode(node.type);
+        const isNodeTrigger = isTriggerNode(node.type);
 
         // Trigger nodes only need outgoing connections
-        if (isTrigger) {
+        if (isNodeTrigger) {
           return !workflow.connections?.[node.name]; // Disconnected if no outgoing connections
         }
 
@@ -315,6 +316,29 @@ export function validateWorkflowStructure(workflow: Partial<Workflow>): string[]
     }
   }
 
+  // Validate active workflows have activatable triggers
+  // Issue #351: executeWorkflowTrigger cannot activate a workflow
+  // It can only be invoked by other workflows
+  if ((workflow as any).active === true && workflow.nodes && workflow.nodes.length > 0) {
+    const activatableTriggers = workflow.nodes.filter(node =>
+      !node.disabled && isActivatableTrigger(node.type)
+    );
+
+    const executeWorkflowTriggers = workflow.nodes.filter(node =>
+      !node.disabled && node.type.toLowerCase().includes('executeworkflow')
+    );
+
+    if (activatableTriggers.length === 0 && executeWorkflowTriggers.length > 0) {
+      // Workflow is active but only has executeWorkflowTrigger nodes
+      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.'
+      );
+    }
+  }
+
   // Validate Switch and IF node connection structures match their rules
   if (workflow.nodes && workflow.connections) {
     const switchNodes = workflow.nodes.filter(n => {