Add the ability to manually link posts to already created Linear issues

By default, Quackback creates an issue in Linear when a new post is made. But what if someone already has an issue in Linear and wants to link it to a new Quackback post? I'm not sure if this is possible or if it would complicate the current setup.

If possible, add a small section in the "Manage" area when viewing a post in the admin. It should display something like "Linear:" with a status of "Linked" or "Not Linked." If linked, show the issue code with a hyperlink; if not, allow it to be linked either through a link or by entering the issue code or number.

You could even color-code it as well; red for unlinked, green for linked.