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>

tests/benchmarks/sample.bench.ts

@@ -0,0 +1,47 @@
+import { bench, describe } from 'vitest';
+
+/**
+ * Sample benchmark to verify the setup works correctly
+ */
+describe('Sample Benchmarks', () => {
+  bench('array sorting - small', () => {
+    const arr = Array.from({ length: 100 }, () => Math.random());
+    arr.sort((a, b) => a - b);
+  }, {
+    iterations: 1000,
+    warmupIterations: 100
+  });
+
+  bench('array sorting - large', () => {
+    const arr = Array.from({ length: 10000 }, () => Math.random());
+    arr.sort((a, b) => a - b);
+  }, {
+    iterations: 100,
+    warmupIterations: 10
+  });
+
+  bench('string concatenation', () => {
+    let str = '';
+    for (let i = 0; i < 1000; i++) {
+      str += 'a';
+    }
+  }, {
+    iterations: 1000,
+    warmupIterations: 100
+  });
+
+  bench('object creation', () => {
+    const objects = [];
+    for (let i = 0; i < 1000; i++) {
+      objects.push({
+        id: i,
+        name: `Object ${i}`,
+        value: Math.random(),
+        timestamp: Date.now()
+      });
+    }
+  }, {
+    iterations: 1000,
+    warmupIterations: 100
+  });
+});