Update .gitignore to exclude TypeScript build info and add dist directory. Expand README with project overview, technology stack, prerequisites, and instructions for running and testing the application.

src/HSchool.Server/Game/GameMetrics.cs

@@ -0,0 +1,38 @@
+using System.Diagnostics.Metrics;
+
+namespace HSchool.Server.Game;
+
+/// <summary>Game-loop counters surfaced in the Aspire dashboard.</summary>
+internal sealed class GameMetrics : IDisposable
+{
+    public const string MeterName = "HSchool.Server.Game";
+
+    private readonly Meter _meter;
+    private readonly Counter<long> _ticks;
+    private readonly Histogram<double> _tickDuration;
+    private readonly UpDownCounter<long> _connectedPlayers;
+    private readonly Counter<long> _snapshotBytes;
+
+    public GameMetrics(IMeterFactory meterFactory)
+    {
+        _meter = meterFactory.Create(MeterName);
+        _ticks = _meter.CreateCounter<long>("hschool.game.ticks", "{tick}", "Simulation steps executed.");
+        _tickDuration = _meter.CreateHistogram<double>("hschool.game.tick.duration", "ms", "Wall time of one simulation step.");
+        _connectedPlayers = _meter.CreateUpDownCounter<long>("hschool.game.players", "{player}", "Currently connected players.");
+        _snapshotBytes = _meter.CreateCounter<long>("hschool.game.snapshot.bytes", "By", "Snapshot bytes pushed to clients.");
+    }
+
+    public void RecordTick(double durationMs)
+    {
+        _ticks.Add(1);
+        _tickDuration.Record(durationMs);
+    }
+
+    public void PlayerJoined() => _connectedPlayers.Add(1);
+
+    public void PlayerLeft() => _connectedPlayers.Add(-1);
+
+    public void SnapshotSent(int bytes, int recipients) => _snapshotBytes.Add((long)bytes * recipients);
+
+    public void Dispose() => _meter.Dispose();
+}