no parallel running to avoid flaky tests

frontend/playwright.config.ts

@@ -3,7 +3,7 @@ import { defineConfig } from "@playwright/test";
 export default defineConfig({
   testDir: "./e2e",
   // Run tests sequentially to avoid database conflicts
-  workers: 12,
+  workers: 1,
   // Ensure tests within a file run in order
   fullyParallel: false,
   webServer: {