chore: bump version to 2.18.8

- Update version from 2.18.7 to 2.18.8
- Add comprehensive CHANGELOG entry for PR #308
- Include rebuilt database with modes field (100% coverage)

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

package.json

@@ -1,6 +1,6 @@
 {
   "name": "n8n-mcp",
-  "version": "2.18.7",
+  "version": "2.18.8",
   "description": "Integration between n8n workflow automation and Model Context Protocol (MCP)",
   "main": "dist/index.js",
   "bin": {