gui: rpc plumbing for settings.changed and grabber.progress

Protocol.hpp gains method-name constants for every RPC the next batch of dialogs
needs (settings.*, limiter.*, schedule.*, queue.*, download.addBatch, grabber.*)
and RpcClient re-broadcasts the two events nothing consumed yet:
event.settings.changed and event.grabber.progress. No behaviour change on its
own — OptionsDialog, SchedulerDialog and GrabberWizard are what actually call
these, landing next.

Co-Authored-By: Claude Sonnet 5 <[email protected]>
Claude-Session: https://claude.ai/code/session_01NSCdCWFXBTSBBK3MzWtJiC

gui/src/rpc/RpcClient.cpp

@@ -106,6 +106,10 @@ void RpcClient::onNotification(const QString &methodName, const QJsonObject &par
         emit speedGlobal(params);
     } else if (methodName == QLatin1String(event::kNotify)) {
         emit notify(params);
+    } else if (methodName == QLatin1String(event::kSettingsChanged)) {
+        emit settingsChanged(params);
+    } else if (methodName == QLatin1String(event::kGrabberProgress)) {
+        emit grabberProgress(params);
     }
 }