Add Prism Launcher support and update flake lock

- Add a new home.prismlauncher module with an enable option and a
  custom package override.
- Enable Prism Launcher for the Garand‑Desktop host and remove the
  previous disabled flag.
- Add the user to the “video” group.
- Remove prismlauncher from the core packages list.
- Bump revisions and hashes for several inputs in flake.lock.
- Fix a trailing newline in the helium AppImage definition.

modules/core/packages/packages.nix

@@ -25,7 +25,6 @@
     exercism = exercism;
     jan = jan;
     lazygit = lazygit;
-    prismlauncher = inputs.prismlauncher-cracked.packages.${system}.default;
     spaceCadetPinball = space-cadet-pinball;
     ttySolitaire = tty-solitaire;
     gimp = gimp;