If POST takes longer than 8 seconds, installer immediately gives up rather than continuing to wait

We had an issue where a user had an infinite loading screen on the part of the installer which autodetects game paths.

There were no relevant errors on the install log, but the browser showed a POST error, as if the python side never responded.

What actually happened was that the python side had no errors, but it took longer than 8 seconds to respond. Because the HTML side gives up after 8 seconds, the HTML side raised an error, but the Python side did not. This was because I implemented the timeout using the native `XMLHttpRequest` timeout functionality, which cancels the POST after a timeout (...or at least I think that's how it works).

The installer should really show an error after 8 seconds (or however many seconds), but continue to listen for the response.

The error message should also be adjusted to tell the user to wait some time in case the operation just takes a long time.

I actually had hard-coded that if the request type was `showFileChooser`, there was no POST timeout, but I feel hard-coding specific requests to not the right way to do this.

A related issue is *why* the game scanning step took so long - the user was using a SSD, and didn't have that many games installed on their computer. It could be:
- my installer is doing something really bad and taking ages
- your computer is slow for some reason
- there is a game which causes the installer's scanning algorithm to give worst-case behavior

The scanning should really give up if it took more than a certain amount of time to scan, as even if scanning fails, the installer can still be used. Or perhaps have a per-directory scan timeout.

The installer also doesn't print how long/which folders were scanned,

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- [ ] Fix POST timeout behavior
- [ ] Investigate slow game scanning
- [x] Set a timeout on game scanning (make sure to only enable this when scanning many paths, not when checking a user-specified path) 4efd0b9f3ef1691ff3c4ac8ec281c343587184da
- [x] Add button to cancel scanning (currently becomes greyed out forever if scanning never finishes) e6371a58aa81bcc1fcbe6ad2bf75cd215feaac26

Untersuchen Sie den Frontend-Code des Installers für die XMLHttpRequest-Timeout-Behandlung, wahrscheinlich in einer JavaScript-Datei, die POST-Anfragen verwaltet. Die Backend-Scan-Logik ist in Python; prüfen Sie die Funktionen zur Spielpfaderkennung. Das Issue erwähnt Commits für Scan-Timeout und Abbrechen-Button; überprüfen Sie diese Änderungen, um den aktuellen Stand zu verstehen. Bestimmen Sie, wie das Timeout geändert werden kann, um die Anfrage nicht abzubrechen, und passen Sie die Fehlermeldungen entsprechend an.

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