Fix buttons rendering with iOS Safari's default blue chrome

globals.scss's button reset only set font: inherit — no appearance
reset, no color fallback. Several buttons only set a background and
relied on inherited text color, which iOS Safari doesn't honor for
unstyled <button> elements, so their labels/icons rendered in Safari's
native blue instead of the theme color:

- .stepperButton in MenuItemCustomizer, MenuList, and basket
- .refreshButton in admin/kitchen
- .addButton in admin/MenuItemForm (color was only set on :hover)

Added explicit `color` to each, and hardened globals.scss's button
reset with `color: inherit` plus `-webkit-appearance: none` /
`appearance: none` as a fallback for any future button that forgets.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01RvYdJ3os7tumimsLdLu2j9

src/styles/globals.scss

@@ -56,8 +56,14 @@ body {
   background: $color-background;
 }
 
+// iOS Safari renders an unstyled <button> with its own native blue text/
+// chrome unless appearance is reset and a color is set explicitly — this
+// is a fallback for any button that forgets to set its own `color`.
 button {
   font: inherit;
+  color: inherit;
+  -webkit-appearance: none;
+  appearance: none;
 }
 
 // Route navigation transitions, powered by the router's defaultViewTransition