Add in-game developer console (MrGameEng.DevConsole)

Core gains a static Log (Debug/Info/Warning/Error + event); the engine
logs key events like scene switches. The console captures Log output
into a 2048-line ring buffer and executes registered commands with
input history (up/down), Tab prefix completion and scrolling
(PageUp/PageDown/End/wheel). Built-ins: help, clear, echo, timescale,
close, quit; games register their own (sample: stress/main/beep).

Console core is pure logic covered by headless tests; the Myra overlay
renders a single label rebuilt only when the Revision counter moves -
an idle or closed console costs nothing per frame. Toggled with the
backquote key; sample gameplay hotkeys are suppressed while open.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

samples/MrGameEng.Sample/Scenes/MainScene.cs

@@ -3,6 +3,7 @@ using Microsoft.Xna.Framework;
 using MrGameEng.Assets;
 using MrGameEng.Audio;
 using MrGameEng.Core;
+using MrGameEng.DevConsole;
 using MrGameEng.Graphics;
 using MrGameEng.Input;
 using MrGameEng.UI;
@@ -113,7 +114,25 @@ public sealed class MainScene : Scene
         panel.Widgets.Add(switchButton);
         desktop.Root = panel;
 
-        UpdateSystems.Add(new PlayerControlSystem(player, actions, audio, beep));
+        // Консоль разработчика (клавиша `) — последней, чтобы рисовалась поверх UI.
+        var console = this.UseDevConsole();
+        console.Register("stress", "switch to the stress scene", (_, _) =>
+        {
+            if (!Context.Scenes.IsTransitioning)
+            {
+                Context.Scenes.Switch(new StressScene(), Transition.Fade(0.8f));
+            }
+        });
+        console.Register("main", "switch to the main scene", (_, _) =>
+        {
+            if (!Context.Scenes.IsTransitioning)
+            {
+                Context.Scenes.Switch(new MainScene(), Transition.Fade(0.8f));
+            }
+        });
+        console.Register("beep", "play the beep sound", (_, _) => audio.Play(beep));
+
+        UpdateSystems.Add(new PlayerControlSystem(player, actions, audio, beep, console));
         UpdateSystems.Add(new BounceSystem(WorldBounds));
         UpdateSystems.Add(new CameraControlSystem(camera, player, input));
         UpdateSystems.Add(new SceneHotkeysSystem(Context, actions, () => new StressScene(), Transition.Fade(0.8f)));