chore: bump version to 2.15.5

Version bump due to functionality changes in Phase 5:

Changes:
- handleDeleteWorkflow now returns deleted workflow data
- handleListWorkflows tags parameter fixed (array → CSV string)
- N8nApiClient.deleteWorkflow return type fixed (void → Workflow)
- WorkflowListParams.tags type corrected (string[] → string)

These are bug fixes and enhancements, not just tests.

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

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

package.json

@@ -1,6 +1,6 @@
 {
   "name": "n8n-mcp",
-  "version": "2.15.4",
+  "version": "2.15.5",
   "description": "Integration between n8n workflow automation and Model Context Protocol (MCP)",
   "main": "dist/index.js",
   "bin": {