feat(minion): enable flatpak

I have some apps that I want to install via flatpak, so let's get and
persist flatpak :)

packetmix/homes/minion/flatpak.nix

···
+# SPDX-FileCopyrightText: 2025 Freshly Baked Cake
+#
+# SPDX-License-Identifier: MIT
+
+{
+  clicks.storage.impermanence.persist.directories = [
+    ".var/app"
+    ".local/share/flatpak"
+  ];
+}

packetmix/systems/minion/flatpak.nix

···
+# SPDX-FileCopyrightText: 2025 Freshly Baked Cake
+#
+# SPDX-License-Identifier: MIT
+
+{
+  services.flatpak.enable = true;
+
+  clicks.storage.impermanence.persist.directories = [
+    "/var/lib/flatpak"
+  ];
+}