Bump version to 0.4.0

The in-game version banner (GameVersion.full) reads config/version from
project.godot; it had lagged at 0.2.0 behind the 0.3.0 tag.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01EznnY8rH2dXhtono1kwsXg

project.godot

@@ -11,7 +11,7 @@ config_version=5
 [application]
 
 config/name="Bullosseum"
-config/version="0.2.0"
+config/version="0.4.0"
 run/main_scene="uid://bmnmenu0intr1"
 config/features=PackedStringArray("4.7", "GL Compatibility")
 boot_splash/bg_color=Color(0, 0, 0, 1)