C0: add GE-Proton to ringtail Steam extraCompatPackages

Lets Subnautica 2 (and any other game) opt into the GE-Proton
build via Steam's per-game compatibility tool override, as a
workaround for the Proton Experimental + DXVK D3D12 Mercuna hang.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

docs/changelog.d/+ringtail-proton-ge.infra.md

@@ -0,0 +1,4 @@
+Add GE-Proton (`pkgs.proton-ge-bin`) to `programs.steam.extraCompatPackages`
+on ringtail. Subnautica 2 hangs at Mercuna plugin init under Proton
+Experimental + DXVK D3D12; GE-Proton is available as a Steam per-game
+compatibility option to work around it.

nixos/ringtail/gaming.nix

@@ -5,6 +5,7 @@
   programs.steam = {
     enable = true;
     dedicatedServer.openFirewall = true;
+    extraCompatPackages = [ pkgs.proton-ge-bin ];
   };
 
   # Proton Experimental ships an accessibility bridge (xalia) that hangs during