refactor: Eliminate DRY violation in n8n API response validation (issue #349)

Refactored defensive response validation from PR #367 to eliminate code duplication
and improve maintainability. Extracted duplicated validation logic into reusable
helper method with comprehensive test coverage.

Key improvements:
- Created validateListResponse<T>() helper method (75% code reduction)
- Added JSDoc documentation for backwards compatibility
- Added 29 comprehensive unit tests (100% coverage)
- Enhanced error messages with limited key exposure (max 5 keys)
- Consistent validation across all list operations

Testing:
- All 74 tests passing (including 29 new validation tests)
- TypeScript compilation successful
- Type checking passed

Related: PR #367, code review findings
Files: n8n-api-client.ts (refactored 4 methods), tests (+237 lines)

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

Co-Authored-By: Claude <noreply@anthropic.com>
Conceived by Romuald Członkowski - www.aiadvisors.pl/en

package.json

@@ -1,6 +1,6 @@
 {
   "name": "n8n-mcp",
-  "version": "2.22.2",
+  "version": "2.22.3",
   "description": "Integration between n8n workflow automation and Model Context Protocol (MCP)",
   "main": "dist/index.js",
   "types": "dist/index.d.ts",