Switch from Evolution to GNOME Calendar module

- Enable `calendar.enable` instead of `evolution.enable` in all host
  system‑modules files.
- Add `modules/core/calendar.nix` defining the calendar option and
  installing GNOME Calendar and Contacts.
- Remove the deprecated `modules/core/evolution.nix` and update
  `core/default.nix` imports accordingly.
- Include the GNOME package set via `./gnome.nix` in
  `modules/core/packages/default.nix`.

modules/core/packages/packages.nix

@@ -16,7 +16,7 @@
   packages = with pkgs; {
     bitwarden = bitwarden-desktop;
     eddieAirVPN = eddie;
-    galculator = galculator;
+    gnomeCalculator = gnome-calculator;
     gedit = gedit;
     iotas = iotas;
     logseq = logseq;