[Mac User] Add more MenuBarOptions + Usability Improvement

[sondermusik]

I`d love to have a MenuBarOption to be able to assign Hotkeys to

1. Toggle Sidebar View
2. Start New Conversation

besides that i noticed

1. page-up/-down in chatView doesn't work for me with fn+arrow keys
2. and long conversations loading slows app down, im not sure, but seems like on opening chatview whole convo is loaded?

these all are quality-of-life requests,
I use & enjoy this app a lot, the new adjustment of the "Copy-Code" Button scrolling with the view is such a great add!!!