feat: enhance workflow validation to prevent broken workflows (v2.6.2)

- Add node type existence validation that catches invalid types
- Fix critical issue: now catches 'nodes-base.webhook' BEFORE database lookup
- Add smart suggestions for common mistakes (webhook → n8n-nodes-base.webhook)
- Add minimum viable workflow validation (prevents single-node workflows)
- Add empty connection detection for multi-node workflows
- Add helper functions for workflow structure examples and fix suggestions
- Prevent AI agents from creating workflows with question mark nodes

This fixes the exact issue where workflows created with 'nodes-base.webhook'
would show as broken (question marks) in the n8n UI.

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

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

package.json

@@ -1,6 +1,6 @@
 {
   "name": "n8n-mcp",
-  "version": "2.6.1",
+  "version": "2.6.2",
   "description": "Integration between n8n workflow automation and Model Context Protocol (MCP)",
   "main": "dist/index.js",
   "scripts": {