gui: fix RpcClient double-free on stop() and the 1000-row list cap

Both found live while building gui/tests/dod's DoD harness, not from reading
the code — see that commit for how.

RpcClient::stop() left conn_ dangling after joining the worker thread: the
thread's own finish() flushes the DeferredDelete stop()'s
connect(&thread_, &QThread::finished, conn_, &QObject::deleteLater) already
posted, so conn_ is gone by the time stop() returns, but nothing cleared the
pointer. Any caller that calls stop() and later lets the client destruct
(the harness's own client.stop() at shutdown; also plain, correct API usage)
hit a double-free in the destructor's leftover `delete conn_`. Caught by
ASan on the very first run that actually exercised the stop-then-destroy
path.

requestInitialList() also called download.list with a hardcoded
`{"limit": 1000}`, silently capping the table at 1000 rows no matter how
many the daemon actually has — download.list.schema.json's own description
says "the GUI pages", not "the GUI takes it all in one call". The
scroll-60fps DoD gate refused to run against mockd --tasks 10000 rather
than "pass" against a 1000-row table, which is what surfaced it.
requestInitialList() now pages (5000 per call, the schema's own max) until
`total` is satisfied, then resets the model once with everything.

Separately: RpcConnection's session.subscribe list never included
event.settings.changed or event.grabber.progress, even though RpcClient has
carried signals for both since the Options/Grabber work — session.subscribe
"replaces the previous selection" and "nothing is delivered until this is
called", so both events were being silently dropped by any real daemon that
enforces the subscription (mockd does; verified live with a second
subscribed client actually receiving event.settings.changed after this
fix, round-tripped through a real veloxd's settings.set). GrabberWizard's
5 s poll fallback is exactly why this went unnoticed until now — it covered
for the missing push the whole time.

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

gui/src/rpc/RpcConnection.cpp

@@ -154,10 +154,12 @@ void RpcConnection::dispatchFrame(const QJsonObject &frame) {
                 socket_->abort();  // version mismatch or refused — bounce and retry
                 return;
             }
-            sendRaw(kSubscribeId, QString::fromLatin1(method::kSessionSubscribe),
-                    QJsonObject{{"events", QJsonArray{event::kTaskAdded, event::kTaskRemoved,
-                                                      event::kTaskState, event::kTaskProgress,
-                                                      event::kSpeedGlobal, event::kNotify}}});
+            sendRaw(
+                kSubscribeId, QString::fromLatin1(method::kSessionSubscribe),
+                QJsonObject{
+                    {"events", QJsonArray{event::kTaskAdded, event::kTaskRemoved, event::kTaskState,
+                                          event::kTaskProgress, event::kSpeedGlobal, event::kNotify,
+                                          event::kSettingsChanged, event::kGrabberProgress}}});
             return;
         }
         if (id == kSubscribeId) {