feat(app): main-menu shell loop wiring; gitignore saves/

Replace App.run with a main-menu shell (New Game / Load / Settings /
Quit) above the game loop, wire SaveCommand + MenuCommand into the
registry with an autosave callback, and remove the now-unused
QuitCommand. Migrate GameTest from QuitCommand to MenuCommand.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Semesterprojekt/.gitignore

@@ -40,3 +40,6 @@ build/
 
 ### Brainstorming visual companion ###
 .superpowers/
+
+# Local save games and settings
+saves/