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/StressScene.cs

@@ -2,6 +2,7 @@ using Friflo.Engine.ECS;
 using Microsoft.Xna.Framework;
 using MrGameEng.Assets;
 using MrGameEng.Core;
+using MrGameEng.DevConsole;
 using MrGameEng.Graphics;
 using MrGameEng.Input;
 using MrGameEng.UI;
@@ -71,6 +72,8 @@ public sealed class StressScene : Scene
         panel.Widgets.Add(backButton);
         desktop.Root = panel;
 
+        this.UseDevConsole(); // поверх UI
+
         UpdateSystems.Add(new BounceSystem(WorldBounds));
         UpdateSystems.Add(new StressCameraSystem(camera, input));
         UpdateSystems.Add(new SceneHotkeysSystem(Context, actions, () => new MainScene(), Transition.Wipe(0.8f, Color.DarkSlateBlue)));