fix: fail cleanly when game data is missing

src/CapySR.Data/GameData.cs

@@ -134,12 +134,15 @@ public sealed partial class GameData
     {
         log ??= _ => { };
 
-        var roots = sources.Where(Directory.Exists).ToArray();
+        var wanted = sources.ToArray();
+        var roots = wanted.Where(Directory.Exists).ToArray();
+
         if (roots.Length == 0)
         {
             throw new DirectoryNotFoundException(
-                "no game data sources found. Clone Dimbreath/turnbasedgamedata and point " +
+                "no game data sources found. Clone Dimbreath/turnbasedgamedata and set Data:Sources " +
-                "Data:Sources at its ExcelOutput folder.");
+                "in config/config.json to its ExcelOutput folder. Looked in: " +
+                (wanted.Length > 0 ? string.Join(", ", wanted) : "nowhere, Data:Sources is empty"));
         }
 
         var data = new GameData(roots);

src/CapySR.GameServer/Program.cs

@@ -30,7 +30,18 @@ logger.LogInformation("protocol: {Count} commands", ProtocolRegistry.Count);
 var handlers = HandlerRegistry.Build(logger);
 logger.LogInformation("handlers: {Handlers} implemented", handlers.HandlerCount);
 
-var world = new GameWorld(config, logger);
+GameWorld world;
+
+try
+{
+    world = new GameWorld(config, logger);
+}
+catch (DirectoryNotFoundException e)
+{
+    // a fresh clone has no game data yet; say so plainly instead of dumping a stack trace
+    logger.LogError("{Message}", e.Message);
+    return 1;
+}
 
 var gateway = new KcpGateway(
     config,
@@ -46,3 +57,5 @@ Console.CancelKeyPress += (_, e) =>
 };
 
 await gateway.RunAsync(cancellation.Token);
+
+return 0;