feat: add PageContainer::getPage

This allows us to directly access a page from outside. This will be
useful for telling the ManagedPackPage who is the window it's on, so
that we can close it when updating :^)

Signed-off-by: flow <flowlnlnln@gmail.com>

launcher/ui/widgets/PageContainer.cpp

@@ -130,6 +130,11 @@ bool PageContainer::selectPage(QString pageId)
     return false;
 }
 
+BasePage* PageContainer::getPage(QString pageId)
+{
+    return m_model->findPageEntryById(pageId);
+}
+
 void PageContainer::refreshContainer()
 {
     m_proxyModel->invalidate();