ci: use repo pnpm 10 (fixes lockfile-ignore + postman-code-generators…

[Jatishchawla]

ci: align workflows to repo pnpm 10 (fix e2e install failure)

What

Switch the nightly-staging-e2e, linter, and deploy-frontend workflows from a hard-pinned pnpm 8 to the repo's declared pnpm 10 (pnpm/action-setup@v4 with no version pin, so it reads the root packageManager). This mirrors the already-passing jest-test.yml.

Why

The e2e pipeline was failing at the Install Dependencies step. Running CI on pnpm 8 while the repo is on pnpm 10 (packageManager: pnpm@10.12.1) caused two problems:

1. Lockfile ignored — WARN Ignoring not compatible lockfile … pnpm-lock.yaml → non-deterministic, full re-resolve.

2. Fatal postinstall crash — pnpm 8 runs every dependency's lifecycle script, including the broken postman-code-generators one:

   error This project's package.json defines "packageManager": "yarn@pnpm@10.12.1" …
   Error: Callback was already called.
   ELIFECYCLE  Command failed with exit code 1.
   

pnpm 10 gates dependency build/postinstall scripts by default, so that script never runs — which is exactly why local installs (pnpm 10) already succeed. Aligning CI to pnpm 10 fixes both the lockfile warning and the crash.

Scope / safety

• Only 3 workflow YAML files changed (8 insertions, 10 deletions). No application, runtime, or dependency code touched.
• jest-test.yml, docs-check.yml, deploy-docs.yml already used pnpm 10 (unchanged).

Testing

• Verified the failure reproduces only under pnpm 8; local pnpm install on pnpm 10 completes successfully (the broken script is gated).
• Full green confirmation will come from the e2e run after this lands (it needs the scheduled/dispatch trigger + staging secrets on the merged branch).