ci: run wrangler through npx so the preview deploy survives pnpm 12

[chybisov]

Which Linear task is linked to this PR?

None — CI infrastructure, found while checking the checks on #874.

Why was it implemented this way?

Every preview deploy has failed since #870 migrated the repo to pnpm 12:

Error: ERR_PNPM_IGNORED_BUILDS
  × adding a new package
  ╰─▶ Ignored build scripts: esbuild@0.28.2, workerd@1.20260508.1
  help: Run "pnpm approve-builds" to pick which dependencies should be allowed to run scripts.

pnpm 12 fails an install whose packages have ignored build scripts. pnpm dlx installs into its own store outside the workspace, so the allowBuilds list in pnpm-workspace.yaml never reaches it — and wrangler needs esbuild and workerd built. The deploy step is the only pnpm dlx call in the workflows; delete-test-app.yaml talks to the Cloudflare API directly and is unaffected.

npx installs with npm, which has no build-script gate, and it is already how the Jumper fork resolved the same breakage after its own pnpm 12 migration.

Alternatives considered

• Add esbuild/workerd to allowBuilds — does not help. The list lives in pnpm-workspace.yaml and a pnpm dlx install never reads it. It would also grant build scripts to the whole workspace to fix one throwaway CLI install.
• pnpm dlx --allow-build=esbuild,workerd — works, but pins the transitive build requirements of wrangler into our workflow. A wrangler bump that adds a third native dependency breaks the deploy again.
• Add wrangler as a devDependency — puts a deploy-only CLI and its native deps into every developer's install.

Visual showcase (Screenshots or Videos)

n/a — no user-facing change.

Checklist before requesting a review

• I have performed a self-review and testing of my code.
• This pull request is focused and addresses a single problem.
• If this PR modifies the Widget API or adds new features that require documentation, I have updated the documentation in the public-docs repository.

Testing

Reproduced locally against the repo's own pnpm 12.3.4, which reproduces the CI error byte for byte:

$ pnpm dlx wrangler@4.90.1 --version
Error: ERR_PNPM_IGNORED_BUILDS
  ╰─▶ Ignored build scripts: esbuild@0.28.2, workerd@1.20260508.1

$ npx -y wrangler@4.90.1 --version
4.90.1

The deploy job is gated on the testing label, so this PR carries it to exercise the changed step in CI.

Note for #874

That PR's red Publish to Cloudflare Pages is this bug, not its own change. Once this merges, its merge ref picks up the fixed workflow and a re-run should go green — nothing to change there.

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