gaming: install Minecraft Bedrock via nix-flatpak

Add the nix-flatpak flake input and wire its NixOS module into the gaming
module to declaratively install io.mrarm.mcpelauncher from Flathub. The
Flatpak build tracks the newer, pairip-protected Bedrock releases ahead of
the nixpkgs mcpelauncher package.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

flake.lock

@@ -137,6 +137,21 @@
         "type": "github"
       }
     },
+    "nix-flatpak": {
+      "locked": {
+        "lastModified": 1783368811,
+        "narHash": "sha256-0H8jDwR4Kegb3heaTrH1ftbgKfZVDT8JE+46uXxDy/Q=",
+        "owner": "gmodena",
+        "repo": "nix-flatpak",
+        "rev": "20d42f0ee98c9fe9f85e8d1de474f1409ed10d05",
+        "type": "github"
+      },
+      "original": {
+        "owner": "gmodena",
+        "repo": "nix-flatpak",
+        "type": "github"
+      }
+    },
     "nixpkgs": {
       "locked": {
         "lastModified": 1784796856,
@@ -203,6 +218,7 @@
         "home-manager": "home-manager",
         "hyprland-preview-share-picker": "hyprland-preview-share-picker",
         "illogical-flake": "illogical-flake",
+        "nix-flatpak": "nix-flatpak",
         "nixpkgs": "nixpkgs",
         "spicetify-nix": "spicetify-nix"
       }