chore: update pre-merge regression-test check to exempt apps/* and test/doc/asset-only PRs

## Summary

The **End-To-End Regression Coverage For Fixes** pre-merge check currently flags PRs that add tests in `apps/website/e2e/` instead of `browser_tests/` and also flags PRs whose only changed files are test, documentation, or asset files. This creates false-positive failures for legitimate changes.

## Requested changes

1. **Ignore `apps/*` paths** — files under any `apps/` sub-directory (e.g. `apps/website/`) live in a separate workspace with their own test conventions and should not be required to add tests to `browser_tests/`.

2. **Ignore PRs that are test/doc/asset-only** — if *all* changed files in the PR match extensions such as `.spec.*`, `.test.*`, `.tests.*`, `.md`, `.png`, `.jpg`, `.svg`, `.webp`, etc., the check should pass automatically, as there is no production code to cover.

## Motivation

Raised in PR #11436 (feat: add demo pages with Arcade embeds at /demos/{slug}), where the E2E tests live at `apps/website/e2e/demos.spec.ts` and the check incorrectly errored because the file is not under `browser_tests/`.

## Suggested exemption rule (pseudo-logic)

```
if all changed files match:
apps/**
OR *.spec.* | *.test.* | *.tests.* | *.md | *.png | *.jpg | *.jpeg | *.svg | *.webp | *.gif
then: skip / pass the regression-test check
```

---

Requested by @christian-byrne — see https://github.com/Comfy-Org/ComfyUI_frontend/pull/11436

┆Issue is synchronized with this [Notion page](https://www.notion.so/Issue-11438-chore-update-pre-merge-regression-test-check-to-exempt-apps-and-test-doc-asset-onl-3486d73d3650814b9da0ccaa271a395e) by [Unito](https://www.unito.io)