feat: add comprehensive performance benchmark tracking system

- Create benchmark test suites for critical operations:
  - Node loading performance
  - Database query performance
  - Search operations performance
  - Validation performance
  - MCP tool execution performance

- Add GitHub Actions workflow for benchmark tracking:
  - Runs on push to main and PRs
  - Uses github-action-benchmark for historical tracking
  - Comments on PRs with performance results
  - Alerts on >10% performance regressions
  - Stores results in GitHub Pages

- Create benchmark infrastructure:
  - Custom Vitest benchmark configuration
  - JSON reporter for CI results
  - Result formatter for github-action-benchmark
  - Performance threshold documentation

- Add supporting utilities:
  - SQLiteStorageService for benchmark database setup
  - MCPEngine wrapper for testing MCP tools
  - Test factories for generating benchmark data
  - Enhanced NodeRepository with benchmark methods

- Document benchmark system:
  - Comprehensive benchmark guide in docs/BENCHMARKS.md
  - Performance thresholds in .github/BENCHMARK_THRESHOLDS.md
  - README for benchmarks directory
  - Integration with existing test suite

The benchmark system will help monitor performance over time and catch regressions before they reach production.

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

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

.github/BENCHMARK_THRESHOLDS.md

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+# Performance Benchmark Thresholds
+
+This file defines the expected performance thresholds for n8n-mcp operations.
+
+## Critical Operations
+
+| Operation | Expected Time | Warning Threshold | Error Threshold |
+|-----------|---------------|-------------------|-----------------|
+| Node Loading (per package) | <100ms | 150ms | 200ms |
+| Database Query (simple) | <5ms | 10ms | 20ms |
+| Search (simple word) | <10ms | 20ms | 50ms |
+| Search (complex query) | <50ms | 100ms | 200ms |
+| Validation (simple config) | <1ms | 2ms | 5ms |
+| Validation (complex config) | <10ms | 20ms | 50ms |
+| MCP Tool Execution | <50ms | 100ms | 200ms |
+
+## Benchmark Categories
+
+### Node Loading Performance
+- **loadPackage**: Should handle large packages efficiently
+- **loadNodesFromPath**: Individual file loading should be fast
+- **parsePackageJson**: JSON parsing overhead should be minimal
+
+### Database Query Performance
+- **getNodeByType**: Direct lookups should be instant
+- **searchNodes**: Full-text search should scale well
+- **getAllNodes**: Pagination should prevent performance issues
+
+### Search Operations
+- **OR mode**: Should handle multiple terms efficiently
+- **AND mode**: More restrictive but still performant
+- **FUZZY mode**: Slower but acceptable for typo tolerance
+
+### Validation Performance
+- **minimal profile**: Fastest, only required fields
+- **ai-friendly profile**: Balanced performance
+- **strict profile**: Comprehensive but slower
+
+### MCP Tool Execution
+- Tools should respond quickly for interactive use
+- Complex operations may take longer but should remain responsive
+
+## Regression Detection
+
+Performance regressions are detected when:
+1. Any operation exceeds its warning threshold by 10%
+2. Multiple operations show degradation in the same category
+3. Average performance across all benchmarks degrades by 5%
+
+## Optimization Targets
+
+Future optimization efforts should focus on:
+1. **Search performance**: Implement FTS5 for better full-text search
+2. **Caching**: Add intelligent caching for frequently accessed nodes
+3. **Lazy loading**: Defer loading of large property schemas
+4. **Batch operations**: Optimize bulk inserts and updates