Configure for atlas/pinj and add Wayland session variables

- Rename hosts/hostname/ to hosts/atlas/
- Replace all <hostname> placeholders with 'atlas'
- Replace all <username> placeholders with 'pinj'
- Set timezone to Europe/Rome (with TODO note to change if needed)
- Set locale to en_US.UTF-8
- Add Wayland session variables (QT_QPA_PLATFORM, MOZ_ENABLE_WAYLAND,
  NIXOS_OZONE_WL) for proper app integration
- Remove placeholder comments that are no longer needed

https://claude.ai/code/session_01UAdmEkSeh9NGPfjRfViLWY

flake.nix

@@ -34,9 +34,8 @@
     mangoModule = assert lib.hasAttrByPath [ "nixosModules" "mango" ] mango;
       mango.nixosModules.mango;
 
-    # IMPORTANT: Replace <hostname> with actual hostname
     commonModules = [
-      ./hosts/<hostname>/hardware-configuration.nix
+      ./hosts/atlas/hardware-configuration.nix
       ./modules/common.nix
       mangoModule
     ];