refactor(app): one idle-loop wake predicate for background results

hasPendingRPCResults() becomes hasPendingBackgroundResults(): the one
check the idle loop makes, every <= 200 ms, for work that finished on a
background thread and still has to be applied by update(). Lanes added
later put their term there. It still covers only the two RPC worker
lanes; no behaviour change.

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

src/main.cpp

@@ -1737,9 +1737,9 @@ int main(int argc, char* argv[])
                 auto sinceLast = std::chrono::duration_cast<std::chrono::milliseconds>(
                                      now - lastPeriodicFrame).count();
 
-                // Immediate triggers: async RPC results, visible notifications, work in progress
+                // Immediate triggers: background results, visible notifications, work in progress
                 // (also what keeps a hidden or occluded window responsive: ~5 fps while it lasts)
-                bool hasImmediateWork = app.hasPendingRPCResults()
+                bool hasImmediateWork = app.hasPendingBackgroundResults()
                                      || app.hasTransactionSendProgress()
                                      || app.isTransactionRefreshInProgress()
                                      || app.isShuttingDown()