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

#### PR Dependency Tree


* **PR #14897** 👈

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

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## 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.
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