chore: update n8n to 1.115.2 and bump version to 2.18.11 (#323)

- Updated n8n to ^1.115.2 (from ^1.114.3)
- Updated n8n-core to ^1.114.0 (from ^1.113.1)
- Updated n8n-workflow to ^1.112.0 (from ^1.111.0)
- Updated @n8n/n8n-nodes-langchain to ^1.114.1 (from ^1.113.1)
- Rebuilt node database with 537 nodes (increased from 525)
- All 1,181 functional tests passing (1 flaky performance test)
- All validation tests passing
- Built and ready for deployment
- Updated README n8n version badge
- Updated CHANGELOG.md

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Co-authored-by: Claude <noreply@anthropic.com>

package.runtime.json

@@ -1,6 +1,6 @@
 {
   "name": "n8n-mcp-runtime",
-  "version": "2.18.10",
+  "version": "2.18.11",
   "description": "n8n MCP Server Runtime Dependencies Only",
   "private": true,
   "dependencies": {