scripts: fix create-host flake.nix insertion point

Fix bug where new hosts were added outside of nixosConfigurations block
instead of inside it.

Issues fixed:
1. Pattern was looking for "packages =" but actual text is "packages = forAllSystems"
2. Replacement was putting new entry AFTER closing brace instead of BEFORE
3. testvm01 was at top-level flake output instead of in nixosConfigurations

Changes:
- Update pattern to match "packages = forAllSystems"
- Put new entry BEFORE the closing brace of nixosConfigurations
- Move testvm01 to correct location inside nixosConfigurations block

Result: nix flake show now correctly shows testvm01 as NixOS configuration

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

flake.nix

@@ -334,7 +334,6 @@
             sops-nix.nixosModules.sops
           ];
         };
-      };
       testvm01 = nixpkgs.lib.nixosSystem {
         inherit system;
         specialArgs = {
@@ -351,6 +350,7 @@
           sops-nix.nixosModules.sops
         ];
       };
+      };
       packages = forAllSystems (
         { pkgs }:
         {