fix(selection): port SmartBox click lighting pulse

Port the retail high/low material-lighting cadence for successful world clicks, keep it instance-scoped in the modern renderer, and restore authored lighting after 0.8 seconds. Correct the selection oracle and pin timing plus per-frame buffer lifecycle with tests.

Co-authored-by: Codex <codex@openai.com>

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

@@ -0,0 +1,75 @@
+using AcDream.App.Rendering.Selection;
+
+namespace AcDream.App.Tests.Rendering;
+
+public sealed class RetailSelectionLightingPulseTests
+{
+    [Fact]
+    public void ClickRunsRetailHighLowHighLowRestoreCadence()
+    {
+        double now = 10d;
+        var pulse = new RetailSelectionLightingPulse(() => now);
+
+        pulse.Start(0x5000_1234u);
+        AssertLighting(pulse, 0x5000_1234u, RetailSelectionLighting.High);
+
+        now = 10.199;
+        pulse.Tick();
+        AssertLighting(pulse, 0x5000_1234u, RetailSelectionLighting.High);
+
+        now = 10.2;
+        pulse.Tick();
+        AssertLighting(pulse, 0x5000_1234u, RetailSelectionLighting.Low);
+
+        now = 10.4;
+        pulse.Tick();
+        AssertLighting(pulse, 0x5000_1234u, RetailSelectionLighting.High);
+
+        now = 10.6;
+        pulse.Tick();
+        AssertLighting(pulse, 0x5000_1234u, RetailSelectionLighting.Low);
+
+        now = 10.8;
+        pulse.Tick();
+        Assert.False(pulse.TryGet(0x5000_1234u, out _));
+    }
+
+    [Fact]
+    public void LongFrameAdvancesOnlyOneRetailGlobalLoopFlip()
+    {
+        double now = 1d;
+        var pulse = new RetailSelectionLightingPulse(() => now);
+        pulse.Start(0x5000_1234u);
+
+        now = 20d;
+        pulse.Tick();
+
+        AssertLighting(pulse, 0x5000_1234u, RetailSelectionLighting.Low);
+    }
+
+    [Fact]
+    public void NewClickRestoresOldTargetAndRestartsHighOnNewTarget()
+    {
+        double now = 4d;
+        var pulse = new RetailSelectionLightingPulse(() => now);
+        pulse.Start(0x5000_0001u);
+
+        now = 4.2;
+        pulse.Tick();
+        AssertLighting(pulse, 0x5000_0001u, RetailSelectionLighting.Low);
+
+        pulse.Start(0x5000_0002u);
+
+        Assert.False(pulse.TryGet(0x5000_0001u, out _));
+        AssertLighting(pulse, 0x5000_0002u, RetailSelectionLighting.High);
+    }
+
+    private static void AssertLighting(
+        RetailSelectionLightingPulse pulse,
+        uint serverGuid,
+        RetailSelectionLighting expected)
+    {
+        Assert.True(pulse.TryGet(serverGuid, out var actual));
+        Assert.Equal(expected, actual);
+    }
+}