services.flatpak.enable = true (set inside core/system/gaming.nix's
mkIf cfg.enable block) ships flatpak but doesn't add any remotes, so
`flatpak install` and the Discover GUI returned empty results until
the user ran the manual `flatpak remote-add` one-liner. nixpkgs has
no declarative remote-add API yet.
Added systemd.services.nomarchy-flathub-init: a Type=oneshot,
RemainAfterExit=true unit that runs
`flatpak remote-add --if-not-exists flathub
https://dl.flathub.org/repo/flathub.flatpakrepo`
after network-online.target. The --if-not-exists flag keeps it
idempotent across reboots and re-runs.
Lives under the gaming preset (where flatpak is wired today); lift
to a dedicated module when another preset needs flatpak.
Closes the "Gaming — declarative flathub remote" Next-column item.
`nix flake check --no-build` clean.
2948dc4dbf