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.

hosts/Garand-Desktop/home-modules.nix

@@ -36,11 +36,12 @@ _: {
   */
   lutris.enable = false; # Lutris: an open gaming platform
   mangohud.enable = true; # MangoHud: Vulkan and OpenGL overlay for monitoring FPS, temperatures, CPU/GPU load and more
+  prismlauncher.enable = true; # Prism Launcher: Minecraft modded launcher
 
   /*
   Media recording and streaming
   */
-  obs-studio.enable = false; # OBS Studio: streaming and recording software
+  obs-studio.enable = true; # OBS Studio: streaming and recording software
 
   /*
   Office suite

hosts/Garand-Desktop/system-modules.nix

@@ -60,7 +60,6 @@ _: {
     /*
     Gaming
     */
-    prismlauncher.enable = false; # Prism Launcher: Minecraft modded launcher
     spaceCadetPinball.enable = true; # SpaceCadet Pinball: classic pinball game
     ttySolitaire.enable = true; # TTY Solitaire: terminal‑based solitaire game
     heroic.enable = false; # Native GOG, Epic, and Amazon Games Launcher for Linux, Windows and Mac