Add Transform and client yaw helpers to Quaternion

Transform holds location, rotation and scale as the client's ArcObjectInfo
does, with parent x local composition (sb.exe 0x6516C0). Quaternion.fromYaw
matches the client's MakeRotateY and getYaw returns the angle it would need.
Nothing uses them yet.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/engine/math/Quaternion.java

@@ -1142,6 +1142,17 @@ public class Quaternion {
         return opposite(this);
     }
 
+    // Client MakeRotateY (Math.dll 0x10002960): w = cos θ/2, y = sin θ/2, radians.
+    // Math rather than FastMath: FastMath.reduceSinAngle mis-reduces angles below -π.
+    public static Quaternion fromYaw(float yaw) {
+        return new Quaternion(0f, (float) Math.sin(yaw * 0.5), 0f, (float) Math.cos(yaw * 0.5));
+    }
+
+    // The angle MakeRotateY would need to produce this rotation; characters send it as one float.
+    public float getYaw() {
+        return 2 * FastMath.atan2(y, w);
+    }
+
     @Override
     public Quaternion clone() {
         try {