feat: move from FantasqueSansMono to IBS Plex and set it as default across the board

modules/nixos/default.nix

@@ -9,5 +9,6 @@
     ./services.nix
     ./sound.nix
     ./system.nix
+    ./theming.nix
   ];
 }

modules/nixos/packages.nix

@@ -72,8 +72,8 @@
     (catppuccin-sddm.override # So SDDM finds the theme files.
       {
         flavor = "frappe";
-        font = "FantasqueSansM Nerd Font";
-        fontSize = "12";
+        font = "IBM Plex Sans";
+        fontSize = "11";
         background = "${./theming/sddm/Background.jpg}";
         loginBackground = true;
       }

modules/nixos/theming.nix

@@ -0,0 +1,12 @@
+{ ... }:
+
+{
+  # Set the default fonts for the system.
+  fonts.fontconfig = {
+    defaultFonts = {
+      serif = [ "IBM Plex Serif" ];
+      sansSerif = [ "IBM Plex Sans" ];
+      monospace = [ "IBM Plex Mono" ];
+    };
+  };
+}