feat(pikachu): add Fabric Minecraft guest

configs/nixos/guests/minecraft.nix

@@ -0,0 +1,48 @@
+{
+  config,
+  lib,
+  ...
+}:
+let
+  cfg = config.guests.minecraft;
+  minecraftUid = config.registry."stable-uid".${config.networking.hostName}.minecraft;
+in
+{
+  options.guests.minecraft.statePath = lib.mkOption {
+    type = lib.types.nullOr lib.types.str;
+    default = null;
+    example = "/srv/minecraft/main";
+    description = "Host path bind-mounted as Minecraft's durable server state.";
+  };
+
+  config = lib.mkIf cfg.enable {
+    assertions = [
+      {
+        assertion = cfg.statePath != null;
+        message = "guests.minecraft.statePath must point at the host directory that stores Minecraft state.";
+      }
+    ];
+
+    registry."stable-uid".${config.networking.hostName}.minecraft = 20008;
+
+    guests.minecraft = {
+      interior = {
+        modules.services.games.minecraft.enable = true;
+        users.users.minecraft.uid = minecraftUid;
+      };
+
+      mounts."/data" = {
+        directory = cfg.statePath;
+        owner = minecraftUid;
+        group = "storage";
+        mode = "0770";
+      };
+
+      limits = {
+        memory = lib.mkDefault "5G";
+        cpu = lib.mkDefault "400%";
+        tasksMax = lib.mkDefault 1024;
+      };
+    };
+  };
+}