send notification when your post is closed or reopened

[cellio]

meta:293842

Community request with moderate support (+5/-0 at time of writing this): send a notification to the author when a post is closed, so that the author can address the problem (for example to clarify or focus a question or explain why it's not a duplicate). Closure is supposed to be actionable, unlike deletion, so while we don't want to send notifications for every state change, this one seems reasonable.

If we do this, we should also send a notification for reopening.

I acknowledge that we have no way for users to opt out of these notifications until we implement https://github.com/codidact/qpixel/issues/1247. I think that's ok; if you're getting flooded with closure notifications, there's probably a deeper issue.