Move hamburger menu items into macOS menubar

Hello! Big fan of the app. One proposal to get more HIG-adherent.

The "hamburger" menu used inside the app is a non-standard macOS interface element, and its items can be moved into the platform's standard menubar (and the hamburger menu then deleted).

- "Help" just links to the DiffusionBee homepage. DiffusionBee doesn't really have a help page today. I'd propose instead adding "Website" and "GitHub Repository" items to the macOS Help menubar.
- "Discord Group" can also be moved to the Help menubar
- "Show Logs" likely makes most sense under the "File" menubar
- "About" can be removed. It's a duplicate of DiffusionBee > About DiffusionBee in the menubar
- "Close" can be removed. It's a duplicate of Cmd-Q, and DiffusionBee > Close