feat(world): Phase G.1 — debug-time override tests + clear-color clamp

Small polish commit:
- Clamp ClearColor inputs to [0, 1] because retail keyframes store
  sun/fog colors pre-multiplied by their brightness scalars, which can
  exceed 1.0; some drivers treat ClearColor > 1 as a saturate-bright
  hint and produce visible color shifts at the edges.
- 4 new tests cover WorldTimeService.SetDebugTime / ClearDebugTime /
  SyncFromServer-clears-override / SetProvider hot-swap.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/AcDream.App/Rendering/GameWindow.cs

@@ -3040,7 +3040,15 @@ public sealed class GameWindow : IDisposable
         var kf = WorldTime.CurrentSky;
         var atmo = Weather.Snapshot(in kf);
         var fogColor = atmo.FogColor;
-        _gl!.ClearColor(fogColor.X, fogColor.Y, fogColor.Z, 1f);
+        // Clamp to 0..1 — keyframes may store over-1 values (retail uses the
+        // dir-bright scalar pre-multiplied into color) and GL's ClearColor
+        // will silently accept them, but some drivers interpret > 1 as
+        // "bright clamp", producing ugly pink/green frames.
+        _gl!.ClearColor(
+            System.Math.Clamp(fogColor.X, 0f, 1f),
+            System.Math.Clamp(fogColor.Y, 0f, 1f),
+            System.Math.Clamp(fogColor.Z, 0f, 1f),
+            1f);
 
         _gl!.Clear(ClearBufferMask.ColorBufferBit | ClearBufferMask.DepthBufferBit);