fix(openwrt): capture apk stderr and run apk update before apk add opkg

apk errors were being silently dropped (stdout only). Run apk update
first and fail with a clear "router may have no internet" message if
it fails, rather than a cryptic exit-1 from apk add.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

core/archipelago/src/api/rpc/middleware.rs

@@ -70,6 +70,7 @@ pub(super) fn sanitize_error_message(msg: &str) -> String {
         "TollGate installation failed",
         "No pre-built TollGate",
         "opkg not found",
+        "apk update failed",
     ];
     for prefix in &user_facing_prefixes {
         if msg.starts_with(prefix) {