Upgrade vitest to v4.0.5 (#26)

Updates vitest from v2.1.8 to v4.0.5. All tests pass successfully with no code changes required.

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

Co-authored-by: Claude <noreply@anthropic.com>

package.json

@@ -40,7 +40,7 @@
     "tsx": "^4.7.0",
     "typescript": "^5.5.4",
     "typescript-eslint": "^8.0.0",
-    "vitest": "^2.1.8"
+    "vitest": "^4.0.5"
   },
   "dependencies": {
     "@modelcontextprotocol/sdk": "^1.20.1",