Add HSchool.Content project for JSONC definitions, catalog, and map validation. Update solution structure to include new content and tests projects. Enhance school management to support mod packs and map instances, ensuring proper loading and validation. Revise documentation to reflect these changes and update tests for new functionality.

src/HSchool.Server/Program.cs

@@ -19,6 +19,7 @@ builder.Services
     .Validate(options => options.GameMinutesPerRealSecond > 0, "Simulation:GameMinutesPerRealSecond must be positive.")
     .Validate(options => GameClock.IsValidStartDate(options.DefaultStartDate), "Simulation:DefaultStartDate is out of range.")
     .Validate(options => !string.IsNullOrWhiteSpace(options.SavesDirectory), "Simulation:SavesDirectory must be set.")
+    .Validate(options => !string.IsNullOrWhiteSpace(options.ModsDirectory), "Simulation:ModsDirectory must be set.")
     .Validate(options => options.SaveIntervalSeconds is > 0 and <= 3600, "Simulation:SaveIntervalSeconds must be between 1 and 3600.")
     .ValidateOnStart();
 
@@ -26,6 +27,7 @@ builder.Services.AddSingleton<GameCommandQueue>();
 builder.Services.AddSingleton<ClientRegistry>();
 builder.Services.AddSingleton<GameMetrics>();
 builder.Services.AddSingleton<SchoolStore>();
+builder.Services.AddSingleton<ModContent>();
 builder.Services.AddSingleton<GameSocketHandler>();
 builder.Services.AddSingleton<GameLoopService>();
 builder.Services.AddHostedService(sp => sp.GetRequiredService<GameLoopService>());