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

src/MrGameEng.Core/GameClock.cs

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+namespace MrGameEng.Core;
+
+/// <summary>
+/// Engine time service: per-frame delta, total elapsed time, time scaling and frame counter.
+/// Advanced once per frame by <see cref="GameHost"/>.
+/// </summary>
+public sealed class GameClock
+{
+    /// <summary>Seconds elapsed since the previous frame, multiplied by <see cref="TimeScale"/>.</summary>
+    public float DeltaTime { get; private set; }
+
+    /// <summary>Seconds elapsed since the previous frame, unaffected by <see cref="TimeScale"/>.</summary>
+    public float UnscaledDeltaTime { get; private set; }
+
+    /// <summary>Total scaled time in seconds since the game started.</summary>
+    public double TotalTime { get; private set; }
+
+    /// <summary>Total unscaled time in seconds since the game started.</summary>
+    public double UnscaledTotalTime { get; private set; }
+
+    /// <summary>Multiplier applied to <see cref="DeltaTime"/>. 0 pauses gameplay, 1 is real time. Never negative.</summary>
+    public float TimeScale
+    {
+        get => _timeScale;
+        set => _timeScale = value < 0f ? 0f : value;
+    }
+
+    /// <summary>Number of completed frames since the game started.</summary>
+    public long FrameCount { get; private set; }
+
+    private float _timeScale = 1f;
+
+    /// <summary>Advances the clock by one frame. Called by the host; games should not call this.</summary>
+    public void Advance(float unscaledDeltaSeconds)
+    {
+        UnscaledDeltaTime = unscaledDeltaSeconds;
+        DeltaTime = unscaledDeltaSeconds * _timeScale;
+        UnscaledTotalTime += unscaledDeltaSeconds;
+        TotalTime += DeltaTime;
+        FrameCount++;
+    }
+}