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.Protocol/Messages.cs

@@ -0,0 +1,37 @@
+namespace HSchool.Protocol;
+
+/// <summary>First frame from the client: protocol version handshake plus display name.</summary>
+public readonly record struct ClientHelloMessage(byte ProtocolVersion, string PlayerName);
+
+/// <summary>
+/// Movement intent for one client frame. <paramref name="Sequence"/> is echoed back
+/// in future snapshots once client-side prediction lands.
+/// </summary>
+public readonly record struct ClientInputMessage(uint Sequence, InputButtons Buttons);
+
+/// <summary>Round-trip probe; the server mirrors <paramref name="ClientTimeMs"/> back untouched.</summary>
+public readonly record struct ClientPingMessage(long ClientTimeMs);
+
+/// <summary>
+/// Sent once per connection, before the first snapshot.
+/// <paramref name="PlayerEntityId"/> is the replication id of this client's own avatar,
+/// so the renderer can tell it apart from everyone else.
+/// </summary>
+public readonly record struct ServerWelcomeMessage(
+    byte ProtocolVersion,
+    uint PlayerEntityId,
+    byte TickRate,
+    float WorldWidth,
+    float WorldHeight);
+
+/// <summary>One entity inside a snapshot. Kept flat and blittable on purpose.</summary>
+public readonly record struct EntitySnapshot(
+    uint Id,
+    EntityKind Kind,
+    float X,
+    float Y,
+    float Radius,
+    uint Color);
+
+/// <summary>Answer to <see cref="ClientPingMessage"/>, carrying the current server tick.</summary>
+public readonly record struct ServerPongMessage(long ClientTimeMs, uint ServerTick);