refactor(omz): move theme selection and untracked files to extraConfig

modules/home-manager/shell.nix

@@ -8,12 +8,14 @@
     syntaxHighlighting.enable = true;
     oh-my-zsh = {
       enable = true;
-      # theme will be set below
+      # add git and agents as plugins
-      theme = "";
       plugins = [ "git" "ssh-agent" "gpg-agent" ];
-    };
+      # everything here lands before `source $ZSH/oh-my-zsh.sh`
+      extraConfig = ''
+        # make omz faster on large repositories
+        DISABLE_UNTRACKED_FILES_DIRTY=true
+
         # only display a fancy theme when glyphs are rendered
-    initContent = lib.mkOrder 550 ''
         if [[ "$TERM" == "linux" || "$TERM" == "screen" ]]; then
           ZSH_THEME="gentoo"
         else
@@ -21,6 +23,7 @@
         fi
       '';
     };
+  };
 
   # set important env vars
   home.sessionVariables = {