Fix: unify font-family across all .button elements

<button> elements don't inherit font-family from parent by default
in all browsers, causing a visible font mismatch between the
link-based buttons (Back To Store, Back To Website, Cancel Order)
and the button-tag-based Save Changes button on the order
confirmation page.

Add `font-family: inherit` to the base `.button, button` rule so
all button elements use the inherited page font (Roboto). Remove the
now-redundant `font-family: $body-font` from the `.primary` rule.

Fixes openfoodfoundation#13688

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: gbathree

app/webpacker/css/darkswarm/ui.scss

@@ -54,6 +54,7 @@
 .button, button {
   @include border-radius(0.5em);
 
+  font-family: inherit;
   outline: none;
 
   &.x-small {
@@ -65,7 +66,6 @@
 }
 
 .button.primary, button.primary {
-  font-family: $body-font;
   background: $orange-450;
   color: white;
 }