chat: fix #includes with include-what-you-use (#2401)

Also use qGuiApp instead of qApp.

Signed-off-by: Jared Van Bortel <jared@nomic.ai>

gpt4all-chat/server.cpp

@@ -1,13 +1,28 @@
 #include "server.h"
-#include "chat.h"
-#include "mysettings.h"
-#include "modellist.h"
 
-#include <QJsonDocument>
+#include "chat.h"
+#include "modellist.h"
+#include "mysettings.h"
+
+#include <QByteArray>
+#include <QDateTime>
+#include <QDebug>
+#include <QHostAddress>
+#include <QHttpServer>
+#include <QHttpServerRequest>
+#include <QHttpServerResponder>
 #include <QJsonArray>
+#include <QJsonDocument>
 #include <QJsonObject>
 #include <QJsonValue>
+#include <QPair>
+#include <Qt>
+#include <QtLogging>
+
 #include <iostream>
+#include <string>
+#include <type_traits>
+#include <utility>
 
 //#define DEBUG