refactor(desktop): extract the launcher payload lifecycle into updater/payload (#6114)

* refactor(desktop): extract the launcher payload lifecycle into updater/payload

Mechanical move out of updater.ts: payload manifest validation, archive
extraction (ditto/7z + mac xattr scrub), prepared-release verification,
payload activation with attempt pre-arming, and the launcher-side
cleanup machinery (deferred failures, retention, cold-start retry sweep,
manual-clear state reset) move to updater/payload.ts. updater.ts
re-exports LauncherPayloadExtractInput so the public surface is
unchanged; orphaned imports are pruned. No test files change: payload
coverage is integration-style and the desktop suite holds at 269.

* test(pack): follow the mac xattr-scrub assertion to updater/payload

release-workflows.test.ts pins the updater-side mac quarantine-xattr
scrub by reading the desktop updater source; the scrub moved to
src/main/updater/payload.ts in the split, so point the read there. The
assertion's intent is unchanged.

Author: PerishCode