feat(system): add gaming preset module

Opt-in `nomarchy.system.gaming.enable` (default false). Wires
`programs.steam` (with `remotePlay` and `localNetworkGameTransfers`
firewall holes opened via `mkDefault`), `programs.gamemode` (the
launching user must be in the `gamemode` group), and
`services.flatpak`.

Two pieces of the original roadmap entry split into separate
Next-column rows so the system-side preset ships now:

  1. Hyprland fullscreen-on-Steam-launch window rule (home-side).
  2. Declarative flathub remote (nixpkgs has no API for this; needs
     either an overlay or a one-shot systemd unit).

The flatpak service is enabled but the user must add flathub
manually after first boot — documented in OPTIONS.md.

docs/OPTIONS.md

@@ -87,6 +87,10 @@ Wired in `features/desktop/waybar/default.nix` (filters the battery widget out o
 
 `int`, default `32`. `XCURSOR_SIZE` when `accessibility.enable = true`. NixOS default is 24; 32 is a safer floor for low-vision users.
 
+### `nomarchy.system.gaming.enable`
+
+`bool`, default `false`. Gaming preset: enables `programs.steam` (with `remotePlay` and `localNetworkGameTransfers` firewall holes opened by `mkDefault`), `programs.gamemode` (the launching user must be in the `gamemode` group), and `services.flatpak`. The flathub remote isn't added declaratively — after first boot, run `flatpak remote-add --if-not-exists flathub https://dl.flathub.org/repo/flathub.flatpakrepo`. The Hyprland fullscreen-on-Steam-launch window rule is a separate roadmap item.
+
 ### `nomarchy.system.containers.enable`
 
 `bool`, default `false`. Rootless Podman with Docker compatibility (`docker` → `podman`), plus `podman-compose`, `podman-tui`, and `dive`.

docs/ROADMAP.md

@@ -24,7 +24,8 @@ Guardrails (apply when adding anything):
 ### Next (bigger lifts that build on Now)
 
 - **Accessibility — home-side companion.** Hyprland-side bits the system preset can't reach: slower `input.repeat_rate` / `repeat_delay` defaults, `SUPER+ALT+S` keybinding to launch Orca, and a high-contrast palette under `themes/palettes/`. Gated on a new `nomarchy.accessibility.enable` mirror of the system option.
-- **Gaming preset.** `programs.steam.enable`, `programs.gamemode.enable`, `services.flatpak.enable` with a curated remote, and a Hyprland window-rule to fullscreen Steam-launched apps.
+- **Gaming — Hyprland window rule.** Companion to the gaming preset: a Hyprland `windowrulev2 = fullscreen, class:^(steam_app_).*$` (or similar) so games launched from Steam grab the whole screen. Lives in `core/home/config/nomarchy/default/hypr/` and gates on a new `nomarchy.gaming.enable` mirror.
+- **Gaming — declarative flathub remote.** `services.flatpak.enable` doesn't ship a declarative remote API in nixpkgs. Either add the `flatpak-managed-install` overlay, write a one-shot systemd unit that runs `flatpak remote-add --if-not-exists flathub …`, or surface the manual step in `nomarchy-welcome`.
 - **First-run welcome wizard.** Extend `nomarchy-welcome` from a one-shot greeter into a guided picker: theme, panel position, monospace font, "what's a sane home.nix to start with?". Runs once, persists "done" in `state.json`.
 - **Plymouth theme variants per palette.** Currently one Plymouth theme; could template per-palette so the boot splash matches the active theme.
 - **`docs/TROUBLESHOOTING.md`.** The five most common rebuild errors (`option ... already declared`, `attribute ... missing`, Stylix target conflicts, home-manager backupFileExtension churn, impermanence path missing) with copy-paste fixes.
@@ -124,6 +125,7 @@ Each PR description should reference the row(s) in `docs/SCRIPTS.md` it closes,
 
 (Move items here when they land — keep them brief, link the commit/PR.)
 
+- _2026-04-26_ — Gaming preset module (`core/system/gaming.nix`). Opt-in `nomarchy.system.gaming.enable` (default false). Wires `programs.steam` (with `remotePlay`/`localNetworkGameTransfers` firewall holes via `mkDefault`), `programs.gamemode`, and `services.flatpak`. Flathub remote and Hyprland window-rule split into separate Next-column rows.
 - _2026-04-26_ — Accessibility preset module (`core/system/accessibility.nix`). New `nomarchy.system.accessibility.{enable,cursorSize}` options (opt-in, default off — accessibility isn't a hardware-derived signal). Enables `services.gnome.at-spi2-core`, installs Orca, and sets `XCURSOR_SIZE=32` (configurable). Hyprland-side companion (key-repeat slowdown, Orca keybinding, high-contrast palette) split into a new Next-column row.
 - _2026-04-26_ — Desktop preset module (`core/system/desktop.nix`). New `nomarchy.system.desktop.enable` option; defaults to `formFactor == "desktop"` (mirror of the laptop preset's auto-enable). Pins `powerManagement.cpuFreqGovernor` to `"performance"` and enables `services.zfs.{autoScrub,trim}` so a future ZFS pool gets sensible maintenance for free.
 - _2026-04-26_ — Laptop preset module (`core/system/laptop.nix`). New `nomarchy.system.laptop.{enable,thermald}` options; `enable` defaults to `formFactor == "laptop"` so the installer's existing `formFactor` write auto-flips it on. Wires TLP (governors + 75/80 charge thresholds), force-disables `power-profiles-daemon`, enables `upower` and `thermald` (x86_64), adds the brightnessctl udev rule for backlight without root, and sets a logind lid-switch policy that defers to `hibernation.enable`. Closes both the Now item and the largest Next item.