Record a video of the install process on all platforms

To graphically show how to use the installer, I think a video is the most effective way, rather than our current list of instructions. Having a recording for each platform would also be useful for explaining on Linux/MacOS as most of us are not familiar with those platforms/don't have a PC on those platforms.

This is also useful when debugging, since users can say "this part at 1:00 in the video doesn't happen", rather just explain that "nothing happens".

I actually recorded a video already just for the "partial manual install" because that is difficult to explain otherwise: https://www.youtube.com/watch?v=Px4JWsSycQE (this video is linked inside the installer)

I wouldn't be too worried about needing to update the video if something changes, since the basic install process hasn't changed in a very long time.

- [ ] Windows Video
- [ ] MacOS Video
- [ ] Linux Video
- [ ] Steam Deck Video
- [ ] This is a big pain point, because many Steam Deck users have a Windows background and are unfamiliar with using the Konsole + Steam Deck's desktop mode + proton/native etc. A video going through what we already have on the wiki would be very useful.
- [ ] This could be done without a steam deck by installing SteamOS on a PC, see [steampowered.com - Build your own Steam Machine](https://store.steampowered.com/steamos/buildyourown)

Das Issue fordert Videoaufnahmen des Installationsprozesses unter Windows, macOS, Linux und Steam Deck. Beginnen Sie mit einer Überprüfung der vorhandenen Wiki-Anleitungen und des verlinkten Videos zur manuellen Teilinstallation. Verwenden Sie Bildschirmaufzeichnungssoftware, um die Schritte aufzunehmen, und stellen Sie sicher, dass Sie dem aktuellen Installer-Workflow folgen. Die Videos sollten auf einer Plattform wie YouTube hochgeladen und in der Projektdokumentation verlinkt werden.

Vom Indexierungsmodell aus dem Issue-Text verfasst.