QTads should open .gam files on macOS

[dfabulich]

I'm on macOS Sonoma 14.2.1 (but I don't think version matters)

To repro:

1. Download QTads, extract the ZIP, and move QTads.app to your Applications folder. Right-click on it and "Open" it.
2. Download Babel31.gam https://ifarchive.org/if-archive/games/tads/Babel31.gam
3. Go to the File menu and select "Open With…"
   Expected: QTads should appear on the list
   Actual: QTads doesn't (Spatterlight does)
4. On the "Open With…" menu, select "Other…". You'll see a dialog, "Choose an application to open the document", pointing at the Applications folder.
   Actual: QTads is greyed out
   Expected: QTads should be selectable

You can work around this by selecting "All Applications" in the "Enable:" dropdown at the bottom of the dialog, then selecting QTads.

[dfabulich]

I think this isn't working because QTads isn't codesigned, but you can workaround it, and you can even set QTads as the default if you Get Info… and "Change All…".