Migrate sequentialthinking and filesystem servers from Jest to Vitest

- Replace Jest dependencies with Vitest and @vitest/coverage-v8
- Update test scripts to use 'vitest run --coverage'
- Create vitest.config.ts for both servers with node environment and coverage settings
- Update all test files:
  - Change imports from '@jest/globals' to 'vitest'
  - Replace jest.mock() with vi.mock()
  - Replace jest.fn() with vi.fn()
  - Update mock clearing/restoring to use vi methods
- Remove jest.config.cjs files
- All 151 tests passing (24 in sequentialthinking, 127 in filesystem)

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

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

src/sequentialthinking/package.json

@@ -17,7 +17,7 @@
     "build": "tsc && shx chmod +x dist/*.js",
     "prepare": "npm run build",
     "watch": "tsc --watch",
-    "test": "jest --config=jest.config.cjs --coverage"
+    "test": "vitest run --coverage"
   },
   "dependencies": {
     "@modelcontextprotocol/sdk": "^1.19.1",
@@ -25,14 +25,11 @@
     "yargs": "^17.7.2"
   },
   "devDependencies": {
-    "@jest/globals": "^29.7.0",
-    "@types/jest": "^29.5.14",
     "@types/node": "^22",
     "@types/yargs": "^17.0.32",
-    "jest": "^29.7.0",
+    "@vitest/coverage-v8": "^2.1.8",
     "shx": "^0.3.4",
-    "ts-jest": "^29.1.1",
-    "ts-node": "^10.9.2",
-    "typescript": "^5.3.3"
+    "typescript": "^5.3.3",
+    "vitest": "^2.1.8"
   }
 }