Update README.md to include project description, developer documentation links, and license information.

src/MrGameEng.Core/ServiceRegistry.cs

@@ -0,0 +1,33 @@
+namespace MrGameEng.Core;
+
+/// <summary>
+/// Minimal service locator used by engine modules to expose their services
+/// (input, audio, assets, …) to scenes and systems without coupling modules to each other.
+/// </summary>
+public sealed class ServiceRegistry
+{
+    private readonly Dictionary<Type, object> _services = new();
+
+    /// <summary>Registers a service instance under type <typeparamref name="T"/>. Throws if already registered.</summary>
+    public void Add<T>(T service) where T : class
+    {
+        if (!_services.TryAdd(typeof(T), service))
+        {
+            throw new InvalidOperationException($"Service of type {typeof(T)} is already registered.");
+        }
+    }
+
+    /// <summary>Returns the registered service of type <typeparamref name="T"/>. Throws if missing.</summary>
+    public T Get<T>() where T : class
+    {
+        return _services.TryGetValue(typeof(T), out var service)
+            ? (T)service
+            : throw new InvalidOperationException($"Service of type {typeof(T)} is not registered.");
+    }
+
+    /// <summary>Returns the registered service of type <typeparamref name="T"/> or null.</summary>
+    public T? GetOrDefault<T>() where T : class
+    {
+        return _services.TryGetValue(typeof(T), out var service) ? (T)service : null;
+    }
+}