chore: bump version to 2.8.0

- Update package.json version from 2.7.23 to 2.8.0
- Update README.md test count from 1,182 to 1,356 tests
- Add comprehensive CHANGELOG entry for v2.8.0
- Document all test improvements and fixes from PR #104

🤖 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": "2.7.23",
+  "version": "2.8.0",
   "description": "Integration between n8n workflow automation and Model Context Protocol (MCP)",
   "main": "dist/index.js",
   "bin": {