chore(deps): pin packageManager to pnpm

[mrgoonie]

Summary

• Pin packageManager to pnpm@10.34.5 so installs resolve a reproducible pnpm version instead of whichever pnpm happens to be installed on the machine. The repo had no packageManager field, so tooling silently followed the global pnpm and drifted between machines.
• Remove the now-redundant version: input from the pnpm/action-setup step(s). pnpm/action-setup aborts with ERR_PNPM_BAD_PM_VERSION ("Multiple versions of pnpm specified") whenever both the workflow version: input and packageManager are set, so leaving both would break CI.

Why this version

10.34.5 matches the pnpm major this repo's CI already installed, so CI behaviour is unchanged. packageManager becomes the single source of truth and the workflow no longer declares a version.

Scope

• This change does not modify pnpm-lock.yaml.
• Changed files:
  • .github/workflows/ci.yml
  • .github/workflows/deploy-mcp.yml
  • .github/workflows/release.yml
  • package.json

Test plan

• CI passes on this PR
• pnpm install --frozen-lockfile still passes