Reorganize services/ into category subfolders

Group service modules by category (media, network, vpn, identity,
dev, desktop) to make the growing services/ dir easier to navigate.
containers.nix stays at the top level since it's a shared backend,
not a single-category service.

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

hosts/jupiter/vm.nix

@@ -7,11 +7,11 @@
   imports = [
     (modulesPath + "/virtualisation/virtualbox-image.nix")
     ../../common.nix              # shared base: user / ssh / nix / firewall
-    ../../services/samba.nix
-    ../../services/avahi.nix
-    ../../services/audiobookshelf.nix
+    ../../services/network/samba.nix
+    ../../services/network/avahi.nix
+    ../../services/media/audiobookshelf.nix
     ../../services/containers.nix
-    ../../services/caddy.nix
+    ../../services/network/caddy.nix
   ];
 
   networking.hostName = "jupiter";