[cechout]

What does this change

The app now checks once per start whether a newer release is out, and offers to install it: the installer and portable builds download their asset from GitHub and replace themselves, the store build asks the Microsoft Store and lets it install.

• an accent pill in the title bar and beside the version in the settings opens the update dialog, with install, a link to install by hand, and skip this version
• the settings expander gains an update card for checking by hand and undoing a skip, and a toggle for the startup check
• the store build takes only the version name from GitHub, so a GitHub release published before the Store version is live is not announced there

Part of #50.

Checklist

• Builds locally (x64, Release)
• Comments and code are in English