Extract Playwright run and screenshot update logic for reuse across website and main frontend projects

## Summary

PR #11527 introduced two GitHub Actions workflows for the website sub-project:

- `.github/workflows/ci-website-e2e.yaml` — runs Playwright E2E/visual tests, deploys HTML reports to Cloudflare Pages, and posts PR status comments.
- `.github/workflows/pr-update-website-screenshots.yaml` — triggered by label or slash command (`/update-website-screenshots`), re-runs visual tests with `--update-snapshots`, commits updated screenshot expectations back to the PR branch.

This logic (Playwright test execution, Cloudflare Pages report deployment, slash-command-triggered snapshot updates, and automated commit-back) is valuable beyond the website sub-project and should be extracted into reusable composite actions or shared workflow templates so that the main frontend project can also benefit.

## Proposed work

- [ ] Extract the Playwright install + run step into a reusable composite action (e.g. `.github/actions/run-playwright`).
- [ ] Extract the Cloudflare Pages report deployment + PR comment update logic into a reusable composite action.
- [ ] Extract the slash-command / label-triggered snapshot update + commit-back pattern into a reusable workflow or composite action.
- [ ] Wire both the website sub-project and the main frontend project to use these shared actions/workflows.

## References

- PR: #11527
- Comment: https://github.com/Comfy-Org/ComfyUI_frontend/pull/11527#issuecomment-3121013508

/cc @DrJKL

┆Issue is synchronized with this [Notion page](https://www.notion.so/Issue-11534-Extract-Playwright-run-and-screenshot-update-logic-for-reuse-across-website-and-main--34a6d73d36508171a75fe035eddcfea5) by [Unito](https://www.unito.io)