style(share): drop divider line from custom-address prefix

The right border on the address prefix read as a stray vertical line
between the domain and the slug. Remove it and rely on the subtle
prefix background alone to separate the two parts.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

apps/client/src/features/share/components/share-alias-section.tsx

@@ -185,7 +185,6 @@ export default function ShareAliasSection({
               fontSize: "var(--mantine-font-size-xs)",
               color: "var(--mantine-color-dimmed)",
               backgroundColor: "var(--mantine-color-default-hover)",
-              borderRight: "1px solid var(--mantine-color-default-border)",
               borderTopLeftRadius: "var(--input-radius)",
               borderBottomLeftRadius: "var(--input-radius)",
             }}