feat(D.2b): Slice 2 — DollCamera (fixed paperdoll ICamera)

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

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

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+using System.Numerics;
+using AcDream.App.Rendering;
+using Xunit;
+
+namespace AcDream.App.Tests.Rendering;
+
+public class DollCameraTests
+{
+    [Fact]
+    public void Eye_position_is_the_retail_camera_offset()
+    {
+        var cam = new DollCamera { Aspect = 100f / 214f };
+        Assert.True(Matrix4x4.Invert(cam.View, out var inv));
+        var eye = inv.Translation;
+        Assert.Equal(0.12f, eye.X, 3);
+        Assert.Equal(-2.4f, eye.Y, 3);
+        Assert.Equal(0.88f, eye.Z, 3);
+    }
+
+    [Fact]
+    public void Projection_is_finite_and_uses_aspect()
+    {
+        var cam = new DollCamera { Aspect = 1.5f };
+        Assert.True(float.IsFinite(cam.Projection.M11));
+        Assert.NotEqual(0f, cam.Projection.M34);   // perspective w = -z term
+    }
+}