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>

core/home/options.nix

@@ -128,5 +128,16 @@
         '';
       };
     };
+
+    gaming = {
+      enable = lib.mkEnableOption ''
+        Gaming preset (home-side companion to nomarchy.system.gaming.enable).
+        Adds a Hyprland window rule that fullscreens windows whose class
+        matches steam_app_* — i.e. games launched through Steam — so they
+        grab the whole screen instead of opening windowed. Set this to the
+        same value as nomarchy.system.gaming.enable; the installer flips
+        both when the Gaming profile is selected.
+      '';
+    };
   };
 }