fix(combat): track targets with retail camera

Port ClientCombatSystem's Keep in View consumer through CameraSet's pivot-to-target boom heading, including the transformed half-metre target offset and melee/missile validity gates. Preserve the existing stateful chase damping and collision architecture, with conformance coverage and named-retail pseudocode.

Co-Authored-By: Codex <codex@openai.com>

tests/AcDream.App.Tests/Rendering/RetailChaseCameraTests.cs

@@ -116,6 +116,31 @@ public class RetailChaseCameraTests
 
     // ── Basis from heading ────────────────────────────────────────────
 
+    [Fact]
+    public void TrackedHeading_UsesPivotToRetailTargetOffsetPoint()
+    {
+        // The target is ten metres east and one metre below the player's
+        // 1.5 metre camera pivot after TrackTarget's 0.5 metre offset.
+        var pivot = new Vector3(0f, 0f, 1.5f);
+        var targetPoint = new Vector3(10f, 0f, 0.5f);
+        Vector3 expected = Vector3.Normalize(new Vector3(10f, 0f, -1f));
+
+        Vector3 heading = RetailChaseCamera.ComputeTrackedHeading(pivot, targetPoint)!.Value;
+
+        Assert.Equal(expected.X, heading.X, 5);
+        Assert.Equal(expected.Y, heading.Y, 5);
+        Assert.Equal(expected.Z, heading.Z, 5);
+    }
+
+    [Fact]
+    public void TrackedHeading_MissingOrCoincidentTarget_FallsBack()
+    {
+        var pivot = new Vector3(1f, 2f, 3f);
+
+        Assert.Null(RetailChaseCamera.ComputeTrackedHeading(pivot, null));
+        Assert.Null(RetailChaseCamera.ComputeTrackedHeading(pivot, pivot));
+    }
+
     [Fact]
     public void Basis_HorizontalHeading_IsOrthonormalAndRightHanded()
     {