feat(release): ship a Linux .deb that updates itself (#13575)

The Linux release build now also makes a .deb in the same electron-builder
run as the AppImage, and the release publishes it. electron-builder lists it
in latest-linux.yml and writes resources/package-type into it, so the app
updates a .deb install through electron-updater, which installs the new .deb
with dpkg. The desktop updater now allows that path.

The .deb uses xz in threaded mode (XZ_DEFAULTS=-T0): 113 MB in place of
141 MB with gzip. The Linux arm64 release job moves to a 16-vCPU Blacksmith
arm64 runner. The download page, README, install guide, and release docs
list the .deb.

Based on community work in #4071, #5139, #4900, and #4887.

Co-authored-by: chukfinley <chuk@chuk.dev>
Co-authored-by: Primož Ajdišek <bigpod@bigpod.si>
Co-authored-by: benthecarman <benthecarman@live.com>
Co-authored-by: NaveDanan <nave0712@gmail.com>
Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>