fix: limit vitest to one worker to avoid 100% CPU

vitest.config.ts

@@ -27,6 +27,8 @@ export default defineConfig({
 			DATABASE_URL: "mysql://root:root@localhost:3306/test",
 		},
 		testTimeout: 10000,
+		maxWorkers: 1,
+		fileParallelism: false,
 		exclude: ["integration/**", "e2e/**", "node_modules/**", ".next/**"],
 		coverage: {
 			// Off unless asked for (`pnpm test:coverage` passes