fix(mobile): default h5 dev proxy to local backend on 8080

Bare npm run dev (including hosted preview sessions) has no portless
route, so the previous default target https://wygj-api.localhost was
unreachable and every API call failed with HTTP 500. scripts/dev.sh now
passes VITE_PROXY_TARGET explicitly, keeping the portless flow intact.

scripts/dev.sh

@@ -249,7 +249,7 @@ PIDS+=("$!")
 
 if using_portless_mobile; then
   portless alias --remove wygj-mobile-uni >/dev/null 2>&1 || true
-  portless run --name wygj-mobile-uni --force npm --prefix mobile-uni run dev &
+  VITE_PROXY_TARGET="${VITE_PROXY_TARGET:-https://wygj-api.localhost}" portless run --name wygj-mobile-uni --force npm --prefix mobile-uni run dev &
 else
   ./scripts/dev-mobile.sh &
 fi