feat(gamecli): add ShipState record struct

GameCli/Ship.cs

@@ -0,0 +1,18 @@
+namespace GameCli;
+
+/// <summary>
+/// Immutable ship pose + velocity in world coordinates.
+/// World is [0,1] × [0,1]. Y increases downward (screen-native).
+/// Angle=0 means "ship pointing up" (main engine points down).
+/// Positive angle rotates clockwise.
+/// </summary>
+public readonly record struct ShipState(
+    float X,
+    float Y,
+    float VX,
+    float VY,
+    float Angle,
+    float AngularVelocity)
+{
+    public static ShipState AtCenter() => new(0.5f, 0.5f, 0f, 0f, 0f, 0f);
+}