Cannot detect Proton in Steam Installation

[Nutik-Wulf]

Describe the bug
Flatpak installation of protontricks cannot detect Proton from within Steam.

To Reproduce
Steps to reproduce the behavior:

1. Ensure within Steam that the default Compatibility Tool is Proton Experimental.
2. Run command protontricks --gui
3. Select an application from the list given.

Expected behavior
Access to the tool's features for protontricks.

System (please complete the following information):

• Distro: Debian 13 Trixie
• Protontricks installation method: Flatpak
• Protontricks version: 1.13.0
• Steam version: Tested both with and without Steam Beta. The outcome is the same. Installed via the DEB file provided on Steam's website.

Additional context
Maybe it's because Steam installs Proton to steamapps/common for me. Attempted toggling Steam Beta, setting $PROTON_VERSION="proton_experimental", overriding a $PROTON_PATH. I have not tested with other versions of proton, though it appears Proton Experimental should be supported.

If the error happens when trying to run a Protontricks command, run the command again using the -vv flag and copy the output!

protontricks (INFO): Running inside Flatpak sandbox, version 1.16.1.
protontricks (INFO): Found Steam directory at /home/[USERNAME]/.local/share/Steam
protontricks (INFO): Using default Steam Runtime at /home/[USERNAME]/.local/share/Steam/ubuntu12_32/steam-runtime
protontricks (INFO): WINETRICKS environment variable is not available. Searching from $PATH.
protontricks (DEBUG): Found Steam library folder /home/[USERNAME]/.local/share/Steam. Is Flatpak path: False, Is XDG Steam path: True.
protontricks (INFO): Found 1 Steam library folders
protontricks (DEBUG): XDG path for xdg-music is /home/[USERNAME]/Music
(... for various folders)
protontricks (DEBUG): XDG path for xdg-videos is /home/[USERNAME]/Videos
protontricks (DEBUG): Following inaccessible paths were found: set()
protontricks (DEBUG): Following paths have been ignored: set()
protontricks (DEBUG): Creating SteamApp from manifest file in /home/[USERNAME]/.local/share/Steam/steamapps/appmanifest_286160.acf
protontricks (DEBUG): Found compatdata directories for app 286160: []
(... for various title IDs)
protontricks (DEBUG): Creating SteamApp from manifest file in /home/[USERNAME]/.local/share/Steam/steamapps/appmanifest_438100.acf
protontricks (DEBUG): Found compatdata directories for app 438100: [PosixPath('/home/[USERNAME]/.local/share/Steam/steamapps/compatdata/438100/pfx')]
protontricks (DEBUG): Including extra compat tool paths provided via env var: /app/share/steam/compatibilitytools.d
protontricks (DEBUG): Parsing custom compatibility tool manifest at /home/[USERNAME]/.local/share/Steam/compatibilitytools.d/LegacyRuntime/compatibilitytool.vdf
protontricks (DEBUG): Found Steam user entries: [{'steamid3': [STEAMID], 'account_name': '[STEAMNAME]', 'timestamp': '1762731173'}]
protontricks (INFO): Currently logged-in Steam user: [STEAMNAME]
protontricks (INFO): Couldn't find custom shortcuts. Maybe none have been created yet?
protontricks (INFO): Using 'yad' as GUI provider
protontricks (DEBUG): Finding Steam compat tool name for appid 2768430
protontricks (DEBUG): Loading appinfo.vdf in /home/[USERNAME]/.local/share/Steam/appcache/appinfo.vdf
protontricks (DEBUG): appinfo.vdf has magic number b')DV\x07'
protontricks (INFO): No compatibility tool found by reading Steam configuration. Using stable version of Proton as fallback.
protontricks (DEBUG): proton_experimental has compat tool aliases ['proton_experimental', 'proton-experimental', 'proton-10.0-3RC']
protontricks (DEBUG): proton_10 has compat tool aliases ['proton_10', 'proton-10', 'proton-10.0-beta']
protontricks (DEBUG): proton_9 has compat tool aliases ['proton_9', 'proton-9', 'proton-9.0-1RC', 'proton-stable', 'proton-next', 'proton_next', 'proton-7.0-1', 'proton-7.0-2', 'proton-7.0-3', 'proton-7.0-4', 'proton-7.0-5', 'proton-7.0-6', 'proton-8.0-1', 'proton-8.0-2', 'proton-8.0-3', 'proton-8.0-4', 'proton-8.0-5', 'proton-8.0RC', 'proton-9.0-2RC', 'proton-9.0-3RC', 'proton-9.0-4RC', 'proton-9.0-4pin']
protontricks (ERROR): Could not find configured Proton installation!
protontricks (ERROR): Active Proton installation could not be found automatically.
Proton installation could not be found!```

Thank you for your hard work on this, by the way! 

[Matoking]

$PROTON_VERSION requires the human-readable name of the Proton installation, in this case Proton Experimental. Does this work?

$ PROTON_VERSION="Proton Experimental" flatpak run com.github.Matoking.protontricks

I'll probably look into making a new Protontricks release later this week with the fix in place. If you've installed the development version (see the README for details) the default Proton detection should work.