feat: add error mode for execution debugging with AI suggestions (#505)

* feat: add error mode for execution debugging with AI suggestions

Add a new `mode='error'` option to n8n_executions action=get that's optimized
for AI agents debugging workflow failures. This mode provides intelligent
error extraction with 80-99% token savings compared to `mode='full'`.

Key features:
- Error Analysis: Extracts error message, type, node name, and parameters
- Upstream Context: Samples input data from upstream node (configurable limit)
- Execution Path: Shows node execution sequence from trigger to error
- AI Suggestions: Pattern-based fix suggestions for common errors
- Workflow Fetch: Optionally fetches workflow for accurate upstream detection

New parameters for mode='error':
- errorItemsLimit (default: 2) - Sample items from upstream node
- includeStackTrace (default: false) - Full vs truncated stack trace
- includeExecutionPath (default: true) - Include node execution path
- fetchWorkflow (default: true) - Fetch workflow for upstream detection

Token efficiency:
- 11 items: ~11KB full vs ~3KB error (73% savings)
- 1001 items: ~354KB full vs ~3KB error (99% savings)

Conceived by Romuald Członkowski - https://www.aiadvisors.pl/en

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

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

* fix: add security hardening to error-execution-processor

- Add prototype pollution protection (block __proto__, constructor, prototype)
- Expand sensitive data patterns (20+ patterns including JWT, OAuth, certificates)
- Create recursive sanitizeData function for deep object sanitization
- Apply sanitization to both nodeParameters and upstream sampleItems
- Add comprehensive unit tests (42 tests, 96% coverage)

Security improvements address code review findings:
- Critical: Prototype pollution protection
- Warning: Expanded sensitive data filtering
- Warning: Nested data sanitization

Concieved by Romuald Członkowski - www.aiadvisors.pl/en

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

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

---------

Co-authored-by: Romuald Członkowski <romualdczlonkowski@MacBook-Pro-Romuald.local>
Co-authored-by: Claude Opus 4.5 <noreply@anthropic.com>

package.json

@@ -1,6 +1,6 @@
 {
   "name": "n8n-mcp",
-  "version": "2.30.2",
+  "version": "2.31.0",
   "description": "Integration between n8n workflow automation and Model Context Protocol (MCP)",
   "main": "dist/index.js",
   "types": "dist/index.d.ts",