Remove manual authcode copy step
This replaces the manual authcode copy step during login, which is extremely annoying on mobile. Now, the server will return back to the Tokodon seamlessly. The authorization page is changed to match:
This is necessary for Pixelfed support (and maybe other Fediverse software) because they can't show the authcode, it only supports callbacks.
If you want to test, it's easiest just to point Firefox or other browsers to your tokodon binary when it asks you what to do with "tokodon" links. If you don't do this, make sure you have the desktop file installed and update your MIME cache. Otherwise, you won't ever get an authcode and it's very annoying