chore(desktop): update Electron 42

[opencode-agent]

Summary

• update Electron from 42.3.3 to 42.8.1
• refresh the Bun lockfile for Electron's current archive extraction dependency
• stay on the existing Electron 42 major while moving to its maintained release

Why

Electron supports only the latest minor release within each supported major line. Electron 42 remains supported, but 42.3.3 is behind the maintained 42.8.1 release and its accumulated Chromium, Node.js, Electron, crash, and memory-safety fixes.

Testing

• bun typecheck (packages/desktop)
• 71 desktop tests passed; draft-store.test.ts could not run on the host Bun because it lacks node:sqlite
• installed Electron binary reported v42.8.1
• main and preload production bundles completed; the full renderer build reached rendering and then exceeded the shared-host timeout
• Prettier and git diff --check

Requested by: @Hona (Luke Parker via Slack)