Use home-manager.sharedModules for shared user config

Replace manual forEachUser pattern with built-in sharedModules for
applying config to all home-manager users. Add automatic garbage
collection of old generations (weekly, older than 7 days) and remove
the now-unnecessary expire-home-manager-generations justfile recipe.

Also update codex PR patch hash (upstream patch was modified).

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

nixos/base.nix

@@ -93,6 +93,5 @@ makeEnable config "myModules.base" true {
 
   programs.dconf.enable = true;
 
-  home-manager.users = forEachUser (import ./home-manager.nix);
   nix.settings.trusted-users = realUsers ++ ["gitea-runner"];
 }