feat: The script is now steamify.sh

- setup-gamescope-boot.sh renamed to steamify.sh; all references updated.
- Releases publish the bundle as steamify.sh and, for older install commands, setup-gamescope-boot.sh.
- The Steamify shortcut runs steamify.sh.

lib/desktop-shortcut.sh

@@ -1,6 +1,6 @@
 #!/bin/bash
 # "Return to Gaming Mode" desktop shortcut and the sudoers rule it needs.
-# Sourced by setup-gamescope-boot.sh; not meant to be run on its own.
+# Sourced by steamify.sh; not meant to be run on its own.
 
 create_desktop_shortcut() {
     # Determine the home directory of the target user