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

hosts/terra/configuration.nix

@@ -43,11 +43,12 @@ in
   programs.nix-ld.enable = true;
 
   # ---- home-manager (user-level config for darman) ----
-  home-manager.useGlobalPkgs = true;
-  home-manager.useUserPackages = true;
-  home-manager.backupFileExtension = "hm-bak";
+  # Base settings (useGlobalPkgs/useUserPackages/backupFileExtension) and the
+  # shared zsh baseline now live in common.nix + home/common.nix, applied to
+  # every host. This just layers terra's desktop/dev-specific profile on top
+  # — home-manager.users.darman.imports merges additively across modules.
   home-manager.extraSpecialArgs = { inherit unstable inputs; };
-  home-manager.users.darman = import ./home.nix;
+  home-manager.users.darman.imports = [ ./home.nix ];
 
   # ---- Boot (UEFI) ----
   boot.loader.systemd-boot.enable = true;