Add MrGameEng.Inspector: in-engine ECS debugger overlay

Introduce a Chrome-DevTools-style ECS inspector in the UI library. The
headless core (ComponentReflector + EcsInspector) enumerates the store's
entities grouped by archetype, reflects a selected entity's components and
fields, and writes simple scalar edits (number/bool/enum) back through a
generic AddComponent — all unit-tested without a GPU. The Myra overlay
(EcsInspectorUi + InspectorSystems) adds a side panel with an
archetypes -> entities -> fields tree, an editable field view, a
world-pick mode with a selection highlight, and a renderer performance
tab; wired via scene.UseInspector(renderer), toggled with F1.

The UI library now references Graphics (for picking, renderer timings and
Transform2D/Sprite). Docs updated.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

tests/MrGameEng.UI.Tests/ComponentReflectorTests.cs

@@ -0,0 +1,89 @@
+using Microsoft.Xna.Framework;
+using MrGameEng.Inspector;
+using Xunit;
+
+namespace MrGameEng.Inspector.Tests;
+
+public class ComponentReflectorTests
+{
+    private enum Mode
+    {
+        Idle,
+        Run,
+    }
+
+    private struct Probe
+    {
+        public int Count;
+        public float Speed;
+        public bool Active;
+        public Mode State;
+        public Vector2 Offset;
+    }
+
+    [Fact]
+    public void Read_ClassifiesFieldKinds()
+    {
+        var rows = ComponentReflector.Read(
+            new Probe
+            {
+                Count = 3,
+                Speed = 1.5f,
+                Active = true,
+                State = Mode.Run,
+                Offset = new Vector2(2f, 4f),
+            }
+        );
+
+        Assert.Equal(FieldKind.Number, Find(rows, "Count").Kind);
+        Assert.Equal(FieldKind.Bool, Find(rows, "Active").Kind);
+        Assert.Equal(FieldKind.Enum, Find(rows, "State").Kind);
+        Assert.Equal(FieldKind.Text, Find(rows, "Offset").Kind);
+        Assert.False(Find(rows, "Offset").Editable);
+        Assert.Equal("Run", Find(rows, "State").Value);
+        Assert.Equal("(2, 4)", Find(rows, "Offset").Value);
+    }
+
+    [Fact]
+    public void TrySet_UpdatesScalarFields()
+    {
+        object boxed = new Probe();
+
+        Assert.True(ComponentReflector.TrySet(boxed, "Count", "42"));
+        Assert.True(ComponentReflector.TrySet(boxed, "Active", "true"));
+        Assert.True(ComponentReflector.TrySet(boxed, "State", "Run"));
+
+        var probe = (Probe)boxed;
+        Assert.Equal(42, probe.Count);
+        Assert.True(probe.Active);
+        Assert.Equal(Mode.Run, probe.State);
+    }
+
+    [Fact]
+    public void TrySet_RejectsUnparseableValue()
+    {
+        object boxed = new Probe();
+        Assert.False(ComponentReflector.TrySet(boxed, "Count", "not-a-number"));
+    }
+
+    [Fact]
+    public void TrySet_RejectsNonScalarOrMissingField()
+    {
+        object boxed = new Probe();
+        Assert.False(ComponentReflector.TrySet(boxed, "Offset", "1,2"));
+        Assert.False(ComponentReflector.TrySet(boxed, "Missing", "1"));
+    }
+
+    private static FieldRow Find(IReadOnlyList<FieldRow> rows, string name)
+    {
+        foreach (var row in rows)
+        {
+            if (row.Name == name)
+            {
+                return row;
+            }
+        }
+
+        throw new Xunit.Sdk.XunitException($"field {name} not found");
+    }
+}