config(topgrade): manage topgrade.toml on both OSes; add package

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

.chezmoidata/packages.yaml

@@ -44,7 +44,8 @@ packages:
       - starship
       # fonts
       - ttf-victor-mono-nerd
-    aur: []
+    aur:
+      - topgrade
     desktop:
       # linux desktop layer (role desktop|laptop)
       pacman:
@@ -83,6 +84,7 @@ packages:
       - glow
       - atuin
       - starship
+      - topgrade
     cask:
       - kitty
       - font-victor-mono-nerd-font