Fixes lobby backgrounds. (#7557)

Content.Server/GameTicking/GameTicker.LobbyBackground.cs

@@ -1,5 +1,6 @@
 using System.IO;
 using System.Linq;
+using Content.Server.GameTicking.Prototypes;
 using Content.Shared.Audio;
 using Robust.Shared.ContentPack;
 using Robust.Shared.Random;
@@ -25,8 +26,11 @@ public sealed partial class GameTicker
 
     private void InitializeLobbyBackground()
     {
-        _lobbyBackgrounds = _resourceManager.ContentFindFiles(new ResourcePath(LobbyScreenPath)).ToList();
-        _lobbyBackgrounds = _lobbyBackgrounds.FindAll(path => WhitelistedBackgroundExtensions.Contains((path.Extension)));
+        _lobbyBackgrounds = _prototypeManager.EnumeratePrototypes<LobbyBackgroundPrototype>()
+            .Select(x => x.Background)
+            .Where(x => WhitelistedBackgroundExtensions.Contains(x.Extension))
+            .ToList();
+
         LobbyBackground = _lobbyBackgrounds.Any() ? _robustRandom.Pick(_lobbyBackgrounds).ToString() : null;
     }
 

Content.Server/GameTicking/Prototypes/LobbyBackgroundPrototype.cs

@@ -0,0 +1,22 @@
+using JetBrains.Annotations;
+using Robust.Shared.Prototypes;
+using Robust.Shared.Utility;
+
+namespace Content.Server.GameTicking.Prototypes;
+
+/// <summary>
+/// Prototype for a lobby background the game can choose.
+/// </summary>
+[Prototype("lobbyBackground")]
+public sealed class LobbyBackgroundPrototype : IPrototype
+{
+    /// <inheritdoc/>
+    [IdDataField]
+    public string ID { get; set; } = default!;
+
+    /// <summary>
+    /// The sprite to use as the background. This should ideally be 1920x1080.
+    /// </summary>
+    [DataField("background", required: true)]
+    public ResourcePath Background = default!;
+}