feat(app): extract ICamera interface from OrbitCamera

Introduce ICamera (View, Projection, Aspect) and make OrbitCamera implement
it. TerrainRenderer.Draw and StaticMeshRenderer.Draw now accept ICamera,
widening the call-site contract while leaving all runtime behavior unchanged.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/AcDream.App/Rendering/ICamera.cs

@@ -0,0 +1,10 @@
+using System.Numerics;
+
+namespace AcDream.App.Rendering;
+
+public interface ICamera
+{
+    Matrix4x4 View { get; }
+    Matrix4x4 Projection { get; }
+    float Aspect { get; set; }
+}

src/AcDream.App/Rendering/OrbitCamera.cs

@@ -2,7 +2,7 @@ using System.Numerics;
 
 namespace AcDream.App.Rendering;
 
-public sealed class OrbitCamera
+public sealed class OrbitCamera : ICamera
 {
     public Vector3 Target { get; set; } = new(96, 96, 0);  // center of a 192x192 landblock
     public float Distance { get; set; } = 300f;

src/AcDream.App/Rendering/StaticMeshRenderer.cs

@@ -73,7 +73,7 @@ public sealed unsafe class StaticMeshRenderer : IDisposable
         };
     }
 
-    public void Draw(OrbitCamera camera, IEnumerable<WorldEntity> entities)
+    public void Draw(ICamera camera, IEnumerable<WorldEntity> entities)
     {
         _shader.Use();
         _shader.SetMatrix4("uView", camera.View);

src/AcDream.App/Rendering/TerrainRenderer.cs

@@ -55,7 +55,7 @@ public sealed unsafe class TerrainRenderer : IDisposable
         _landblocks.Add(gpu);
     }
 
-    public void Draw(OrbitCamera camera)  // ICamera in Task 5
+    public void Draw(ICamera camera)
     {
         _shader.Use();
         _shader.SetMatrix4("uView", camera.View);