Enable i3 smart gaps

i3.nix

@@ -15,7 +15,11 @@ in {
     config = {
       defaultWorkspace = "workspace number 1"; # defaults to 10 for some reason
       modifier = mod;
-      gaps.inner = 12;
+      # i3-gaps-specific configuration
+      gaps = {
+        inner = 12;
+        smartGaps = true;
+      };
       startup = [
         {
           command = "systemctl --user restart polybar";