feat(gaming): add nomarchy.gaming.enable home-side window rule

Mirror of nomarchy.system.gaming.enable. When on, injects a Hyprland
windowrulev2 = fullscreen, class:^(steam_app_).*$ so games launched
through Steam grab the whole screen instead of opening windowed.

Gated via lib.mkIf so the rule is absent when the option is off
(AGENT.md guardrail: features must be option-gated). The rule is
appended to wayland.windowManager.hyprland.extraConfig (types.lines)
so it composes cleanly with the existing source-line entry point in
features/desktop/hyprland/default.nix.

Closes the "Gaming - Hyprland window rule" Next-column roadmap row.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

docs/ROADMAP.md

@@ -24,7 +24,6 @@ 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 — 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`.
 - **Plymouth theme variants per palette.** Currently one Plymouth theme; could template per-palette so the boot splash matches the active theme.
 
@@ -137,6 +136,7 @@ Nomarchy is moving away from being a "flavor" of Omarchy to its own distinct ide
 
 (Move items here when they land — keep them brief, link the commit/PR.)
 
+- _2026-04-30_ — Gaming home-side companion. New `nomarchy.gaming.enable` option (mirror of `nomarchy.system.gaming.enable`) and `core/home/gaming.nix` module that injects a Hyprland `windowrulev2 = fullscreen, class:^(steam_app_).*$` so Steam-launched games grab the whole screen. Closes the "Gaming — Hyprland window rule" Next-column row.
 - _2026-04-26_ — Default to highest resolution (`highres`) for monitors. Updated `features/desktop/hyprland/config/monitors.conf` and forced it in the live ISO (`nomarchy-live`) to resolve issues where some hardware would default to a low resolution (1024x768).
 - _2026-04-26_ — First-run welcome wizard (`nomarchy-welcome`). Extended from a one-shot greeter into a guided picker for theme, font, and panel position. Added Step 4 to generate a starter `home.nix` if missing. State is now persisted in `state.json` via `.welcome_done`. Added `nomarchy.panelPosition` option to Waybar.
 - _2026-04-26_ — Multi-disk BTRFS support in the installer. Added `installer/disko-btrfs-multi.nix` template and updated `installer/install.sh` to allow selecting multiple drives via `gum choose --no-limit`. Implements BTRFS "single" data + RAID1 metadata across multiple LUKS-encrypted drives.