clanCore: refactor flake-module.nix into smaller files

nixosModules/flake-module.nix

@@ -1,6 +1,13 @@
-{ ... }: {
+{ inputs, self, ... }: {
   flake.nixosModules = {
     hidden-ssh-announce.imports = [ ./hidden-ssh-announce.nix ];
     installer.imports = [ ./installer ];
+    clanCore.imports = [
+      inputs.sops-nix.nixosModules.sops
+      ./clanCore
+      ({ pkgs, lib, ... }: {
+        clanCore.clanPkgs = lib.mkDefault self.packages.${pkgs.hostPlatform.system};
+      })
+    ];
   };
 }