feat: Rename to Steamify CachyOS

Menu header, shortcut, release titles, README and AGENTS.md. Repository, script and URLs keep the name cachyos-gamescope-boot.

assets/steam-gaming-settings.svg

@@ -1,5 +1,5 @@
 <?xml version="1.0" encoding="UTF-8" standalone="no"?>
-<!-- Icon for the "SteamOS Setup Wizard" shortcut of cachyos-gamescope-boot.
+<!-- Icon for the "Steamify CachyOS" shortcut (cachyos-gamescope-boot).
      Derived from Valve's steam-gaming-return.svg (steamdeck-kde-presets,
      GPL-2.0): the Return to Gaming Mode arrow replaced by a gear. -->
 <svg