ci: replace npx with pnpx for wrangler in ci-deploy-preview workflow

## Summary

In `.github/workflows/ci-deploy-preview.yaml` (Line 135), the `deploy-production` job uses `npx wrangler@^4.0.0` to deploy to Cloudflare Pages. This repository mandates `pnpx` (or `pnpm dlx`) as the package manager and `npx` should not be used.

## Change Required

```yaml
# Before
npx wrangler@^4.0.0 pages deploy dist \

# After
pnpx wrangler@^4.0.0 pages deploy dist \
```

## Context

- Raised in PR #11118 (comment: https://github.com/Comfy-Org/ComfyUI_frontend/pull/11118#discussion_r3068918464)
- Acknowledged as a valid non-blocking nit by @christian-byrne
- Low priority; `npx` works correctly in CI runners but is inconsistent with repo tooling policy

## References
- PR: https://github.com/Comfy-Org/ComfyUI_frontend/pull/11118
- Comment: https://github.com/Comfy-Org/ComfyUI_frontend/pull/11118#discussion_r3068918464

/cc @christian-byrne

┆Issue is synchronized with this [Notion page](https://www.notion.so/Issue-11537-ci-replace-npx-with-pnpx-for-wrangler-in-ci-deploy-preview-workflow-34a6d73d365081389ab7c067174e51b4) by [Unito](https://www.unito.io)