Dark Mode bugs

Created by: taylorsperry

Collecting two feedback items related to theme/dark mode that could potentially be addressed simultaneously:

https://github.com/sourcegraph/sourcegraph/issues/28868

According to our keyboard shortcut menu, toggling the color scheme should work with Alt + T. This works on Windows machines, but not Macs.

From a customer, theme seems to switch back to dark mode even when light mode is selected:

Stop changing my theme to dark mode default is mac os and chrome browser OS comes in default configuration (so apple decides initial configuration), engineers are free to change that we do not set theme by default (I used to use dark, but after switching laptop it's light, same as OS) for me it is always light and on old laptop it was persistently dark I don't think we clear cookies or local storage before switching theme