build(deps): refresh pnpm and artifact actions

[steipete]

What Problem This Solves

Refreshes pinned CI tooling after the main Telegram packaging repair.

User Impact

Artifact transfers gain the upstream HTTP 429 retry fix, and RTT jobs receive current pnpm fixes while preserving their existing major versions and Node runtime floors.

Why This Change Was Made

Update pnpm 12.5.1 to 12.10.1 for RTT jobs and pnpm 11.27.1 to 11.28.5 for Crabbox hydration. Update upload-artifact 7.0.1 to 7.0.2 and download-artifact 8.0.1 to 8.0.2. Keep the workflow contract and changelog in sync. No package version change or new dependencies.

Evidence

• pnpm 12.10.1 accepts a synthetic lockfile generated by 12.5.1 under the workflow's frozen-install flags, with byte-identical lockfile output.
• pnpm 11.28.5 starts successfully under Node 24.
• All 232 script tests (two workers), data/README validation, and actionlint pass.
• Independent Codex autoreview: no actionable P0–P2 findings.
• Checks ran locally under nice -n 19 after Crabbox hit fleet capacity and its AWS allocation timed out.