fix(editor): cross browser test stability (#14897)

#### PR Dependency Tree


* **PR #14897** 👈

This tree was auto-generated by
[Charcoal](https://github.com/danerwilliams/charcoal)

<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->
## Summary by CodeRabbit

* **Bug Fixes**
* Improved reliability of shape and connector detection by forcing full
DOM renders during waits.
* Fixed race conditions in code-block theme loading and cleanup when
components unmount.
* Refined viewport element discovery to correctly handle
rotated/canvas-layer elements and avoid stale DOM removal.

* **Tests**
  * Increased polling timeouts and retries to reduce flakiness.
* Disabled per-file parallelism and ensured test setup performs full
cleanup before starting; extended test timeout.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->

packages/frontend/apps/electron/vitest.config.ts

@@ -23,7 +23,7 @@ export default defineConfig({
   test: {
     setupFiles: [resolve(rootDir, './scripts/setup/global.ts')],
     include: ['./test/**/*.spec.ts'],
-    testTimeout: 5000,
+    testTimeout: 30000,
     pool: 'forks',
     maxWorkers: 1,
     coverage: {