feat(desktop): shrink Stylix font sizes for the laptop panel

The graphical layer inherited Stylix's default font sizes, which read
oversized on this display. Step them down a point across applications,
desktop, popups, and the terminal.

modules/desktop/theming.nix

@@ -40,10 +40,21 @@ in
         size = 24;
       };
 
-      fonts.monospace = {
+      fonts = {
+        monospace = {
           package = pkgs.jetbrains-mono;
           name = "JetBrains Mono";
         };
+
+        # A step below Stylix's defaults (applications 12, desktop/popups 10,
+        # terminal 12), which read oversized on this display.
+        sizes = {
+          applications = 10;
+          desktop = 9;
+          popups = 9;
+          terminal = 10;
+        };
+      };
     };
 
     home-manager.users.${user} = {