home-manager: enable for darman on every host, not just terra

terra was the only host with real ~/.zshrc/.zshenv (via home-manager),
so it never hit the plain-zsh zsh-newuser-install wizard that shows up
on first login everywhere else. Wire home-manager.nixosModules.home-manager
into jupiter/neptun/mars/mercury (+ mercury-vm/jupiter-vbox test targets)
and give darman terra's shared zsh baseline via home/common.nix, imported
from common.nix. terra's own home.nix now only carries its
desktop/dev-specific profile (Hyprland, alacritty, git identity, direnv,
dev packages) layered on top via home-manager.users.darman.imports.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Du1WQRk1F8DenrPhf8TofF

flake.nix

@@ -80,6 +80,7 @@
           modules = [
             disko.nixosModules.disko
             sops-nix.nixosModules.sops
+            home-manager.nixosModules.home-manager
             ./hosts/jupiter/configuration.nix
           ];
         };
@@ -91,6 +92,7 @@
           modules = [
             disko.nixosModules.disko
             sops-nix.nixosModules.sops
+            home-manager.nixosModules.home-manager
             ./hosts/neptun/configuration.nix
           ];
         };
@@ -117,6 +119,7 @@
           modules = [
             disko.nixosModules.disko
             sops-nix.nixosModules.sops
+            home-manager.nixosModules.home-manager
             ./hosts/mars/configuration.nix
           ];
         };
@@ -131,6 +134,7 @@
           modules = [
             (nixpkgs + "/nixos/modules/installer/sd-card/sd-image-aarch64.nix")
             sops-nix.nixosModules.sops
+            home-manager.nixosModules.home-manager
             ./hosts/mercury/configuration.nix
           ];
         };
@@ -143,6 +147,7 @@
           inherit system;   # x86_64-linux, fast to build/boot with KVM
           modules = [
             (nixpkgs + "/nixos/modules/virtualisation/qemu-vm.nix")
+            home-manager.nixosModules.home-manager
             ./common.nix
             ./services/network/unbound.nix
             ./services/network/pihole.nix
@@ -169,7 +174,10 @@
         jupiter-vbox = nixpkgs.lib.nixosSystem {
           inherit system;
           specialArgs = { inherit inputs; };
-          modules = [ ./hosts/jupiter/vm.nix ];
+          modules = [
+            home-manager.nixosModules.home-manager
+            ./hosts/jupiter/vm.nix
+          ];
         };
 
         # Custom kexec installer with our SSH key baked in, for headless install