OpenEnsemble Desktop 0.7.0

OpenEnsemble Desktop 0.7.0 adds a Linux AppImage and completes the Windows/Linux
GitHub release channel.

• The installed Windows app and Linux AppImage check for updates 15 seconds
  after startup and every six hours. Updates install only after you choose
  Update and restart.
• Linux replaces the AppImage at its original path and reopens after quitting.
  A failed copy leaves the current installation intact. Settings, sign-in
  storage and local files retain their existing locations.
• The OE sign-in page, Settings → Profile, and public download page select the
  installer for your browser's operating system. Both platform choices remain
  available.
• The bundled Electron runtime is updated to 44.10.0, and dependency security
  fixes are included.

Windows: open OpenEnsemble-Setup-0.7.0-x64.exe and follow the installer.
Linux: save OpenEnsemble-0.7.0-x86_64.AppImage in a writable folder, enable
execution in its Properties, then open it. Select your existing OE server and
sign in. These downloads install the client, not the OE server.

Windows installers are unsigned. Native Windows installation and the complete
Windows upgrade/relaunch flow still require device acceptance. Linux update
acceptance and automated validation are recorded with the local release receipt.

The .yml and .blockmap files are updater metadata; users only need the .exe
or .AppImage. SHA256SUMS.txt contains checksums for the release assets.