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>

CLAUDE.md

@@ -19,7 +19,8 @@ docs/     architecture, conventions, roadmap (Russian)
 Engine modules: `Core` (game loop, ECS world, scenes, time), `Graphics` (custom batched
 renderer, camera, sprites), `Input`, `Audio`, `Assets` (runtime loading, no content
 pipeline), `Assets.Generator` (Roslyn source generator for typed asset handles),
-`UI` (Myra integration: `scene.UseUI()` after `UseRenderer2D()`).
+`UI` (Myra integration: `scene.UseUI()` after `UseRenderer2D()`), `DevConsole`
+(in-game console capturing `Core.Log`; `scene.UseDevConsole()` last in OnLoad).
 Dependency rule: every module may depend only on `Core`; `Core` depends only on
 MonoGame and Friflo.Engine.ECS. `Assets.Generator` is a netstandard2.0 analyzer.
 Documented exception: Myra renders with its own SpriteBatch internally.