add homelab flake

flake.nix

@@ -1 +1,69 @@
-# TODO: Define the homelab NixOS flake.
+{
+  description = "Homelab NixOS configuration";
+
+  inputs = {
+    nixpkgs.url = "github:NixOS/nixpkgs/nixos-25.11";
+
+    disko = {
+      url = "github:nix-community/disko";
+      inputs.nixpkgs.follows = "nixpkgs";
+    };
+
+    home-manager = {
+      url = "github:nix-community/home-manager/release-25.11";
+      inputs.nixpkgs.follows = "nixpkgs";
+    };
+
+    sops-nix = {
+      url = "github:Mic92/sops-nix";
+      inputs.nixpkgs.follows = "nixpkgs";
+    };
+  };
+
+  outputs =
+    inputs@{
+      nixpkgs,
+      disko,
+      home-manager,
+      sops-nix,
+      ...
+    }:
+    let
+      system = "x86_64-linux";
+
+      mkHost =
+        hostModule:
+        nixpkgs.lib.nixosSystem {
+          inherit system;
+          specialArgs = {
+            inherit inputs;
+          };
+
+          modules = [
+            ./modules/base.nix
+            ./modules/gc.nix
+            ./modules/users.nix
+            ./modules/ssh.nix
+            ./modules/tailscale.nix
+
+            disko.nixosModules.disko
+            sops-nix.nixosModules.sops
+            home-manager.nixosModules.home-manager
+
+            {
+              home-manager.useGlobalPkgs = true;
+              home-manager.useUserPackages = true;
+              home-manager.users.admin = import ./home/admin.nix;
+            }
+
+            hostModule
+          ];
+        };
+    in
+    {
+      nixosConfigurations = {
+        yggdrasil = mkHost ./hosts/yggdrasil;
+        midgard = mkHost ./hosts/midgard;
+      };
+    };
+}