Desktop release builds: Linux AppImage, Windows exe and macOS app via tools/build_desktop.py

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/main.rs

@@ -1,4 +1,6 @@
 // DungeonCraft – dungeon building & defence in the browser (Rust + macroquad, WASM).
+// Windows release builds are a window program: no console opens beside the game
+#![cfg_attr(all(windows, not(debug_assertions)), windows_subsystem = "windows")]
 
 mod achievements;
 mod ai;