fix(mobile): white text sits on the contrast-safe accent fill (M7)

Primary buttons, selected segments and context chips use accent-fill, as on
the web, so their labels meet WCAG AA contrast.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

apps/mobile/src/app/(tabs)/index.tsx

@@ -117,7 +117,7 @@ function Chips({
                 height: 38,
                 paddingHorizontal: 14,
                 borderRadius: 999,
-                backgroundColor: on ? colors.accent : colors.surface2,
+                backgroundColor: on ? colors['accent-fill'] : colors.surface2,
                 borderWidth: 1,
                 borderColor: on ? colors.accent : colors.line,
               }}