Add hidden dev debug console (v0.5.0)

play-dev.bat

@@ -0,0 +1,8 @@
+@echo off
+rem MeatSlicer dev launcher - enables the hidden debug console (?dev=1).
+cd /d %~dp0
+start "MeatSlicer server" /min python tools\serve_game.py --port 8123
+timeout /t 1 /nobreak >nul
+start "" "http://localhost:8123/?dev=1"
+echo MeatSlicer running at http://localhost:8123/?dev=1  [debug console: ` key]
+echo Close the minimized "MeatSlicer server" window to stop it.