Switch RetroArch to flatpak for Ubuntu 25.04 compatibility

Closes #438

bin/omakub-sub/install.sh

@@ -10,7 +10,7 @@ CHOICES=(
   "Mainline Kernels  Install newer Linux kernels than Ubuntu defaults"
   "OBS Studio        Record screencasts with inputs from both display + webcam"
   "Ollama            Run LLMs, like Meta's Llama3, locally"
-  "Retroarch         Play retro games [Incompatible w/ 25.04]"
+  "Retroarch         Play retro games"
   "Spotify           Stream music from the world's most popular service"
   "Steam             Play games from Valve's store"
   "VirtualBox        Virtual machines to run Windows/Linux"

install/desktop/optional/app-retroarch.sh

@@ -1,14 +1 @@
-sudo add-apt-repository -y ppa:libretro/stable
-sudo apt update -y
-sudo apt install -y retroarch retroarch-assets
-
-cat <<EOF >~/.local/share/applications/Retroarch.desktop
-[Desktop Entry]
-Name=RetroArch
-Exec=/usr/bin/retroarch
-Type=Application
-Icon=/home/$USER/.local/share/omakub/applications/icons/Retroarch.png
-Comment=Play retro games
-Categories=Game;Emulator;
-Terminal=false
-EOF
+flatpak install -y flathub org.libretro.RetroArch

uninstall/app-retroarch.sh

@@ -1,5 +1 @@
-sudo add-apt-repository -y --remove ppa:libretro/stable
-sudo apt update -y
-sudo apt remove -y retroarch retroarch-assets
-sudo apt autoremove -y
-rm ~/.local/share/applications/Retroarch.desktop
+flatpak uninstall -y flathub org.libretro.RetroArch