Fix surface filtering in user settings and welcome surface

The /api/v1/surfaces endpoint doesn't return source field, so
filter by route pattern (/s/ prefix) instead of source !== 'core'.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/js/sw/surfaces/welcome/index.js

@@ -16,7 +16,7 @@ function WelcomeSurface() {
 
     useEffect(() => {
         sw.api.get('/api/v1/surfaces').then(list => {
-            setSurfaces((list || []).filter(s => s.source !== 'core'));
+            setSurfaces((list || []).filter(s => s.route?.startsWith('/s/')));
         }).catch(() => {});
     }, []);