fix(desktop): stop AppImage updates hanging on quit and deleting the app (#1485)

* fix(desktop): disable auto-install on quit for AppImage only

electron-updater's AppImageUpdater.doInstall() uses execFileSync with APPIMAGE_EXIT_AFTER_INSTALL when autoInstallOnAppQuit is true. For AppImages, this blocks the old process indefinitely because the new process has no installer step to exit from — the mv already completed the install.

Scoped to AppImage only (process.platform === 'linux' && process.env.APPIMAGE). .deb/.rpm/Windows/macOS keep auto-install-on-quit working as before.

* fix(desktop): keep AppImage filename stable across updates

electron-updater renames a versioned AppImage to a new path on update and
unlinks the old one. That orphaned the previous binary, broke desktop
shortcuts, and dangled the ~/.local/bin/paseo CLI symlink, which points at
$APPIMAGE. Dropping ${version} from the AppImage artifactName makes the
updater overwrite the file in place instead; deb/rpm keep versioned names.

Also documents why AppImage must not auto-install on quit (the blocking
execFileSync gated on APPIMAGE_EXIT_AFTER_INSTALL, honored only by
AppImageLauncher) and extracts that gate into a unit-tested helper.

---------

Co-authored-by: Mohamed Boudra <boudra.moha@gmail.com>

packages/desktop/electron-builder.yml

@@ -52,6 +52,13 @@ linux:
     - deb
     - rpm
     - tar.gz
+appImage:
+  # Keep the AppImage filename stable across versions (no ${version}) so
+  # electron-updater overwrites the file in place instead of renaming it to a new
+  # versioned path. A rename orphans the old binary, breaks desktop shortcuts, and
+  # dangles the ~/.local/bin/paseo CLI symlink, which points at $APPIMAGE. The
+  # version stays discoverable via the release tag and the in-app version.
+  artifactName: "Paseo-${arch}.${ext}"
 win:
   artifactName: "Paseo-Setup-${version}-${arch}.${ext}"
   icon: assets/icon.ico