style(design-system): normalize exact-match border-radius literals to tokens

Mechanical sweep for border-radius: 4px/8px/12px/13px/999px replaced
with var(--radius-xs/sm/md/lg/full, <same value>) across src/app.
Only exact matches to existing token values were touched (20px, 16px,
10px, 6px, 3px, 2px etc. were left as-is since no token maps to them
without a visible size change on at least one tenant theme — see
docs/UI-DESIGN-REVIEW.md).

src/app/components/delivery-selector/delivery-selector.component.scss

@@ -5,7 +5,7 @@
 .delivery-selector {
   margin-top: 12px;
   padding: 12px;
-  border-radius: 12px;
+  border-radius: var(--radius-md, 12px);
   border: 1px solid #d3dad9;
   background: #fafbfb;
 }
@@ -48,7 +48,7 @@
   display: inline-flex;
   align-items: center;
   padding: 6px 10px;
-  border-radius: 999px;
+  border-radius: var(--radius-full, 999px);
   font-size: var(--font-size-sm, 0.8125rem);
   font-weight: 700;
 }