Add BlueSky/atproto integration

[pushcx]

Like Mastodon, BlueSky is another plausibly-successful successor to Twitter (RIP). So let’s mirror that functionality from #1175 to support it.

A couple of these to-do list items I have to do, but I hope someone would like to PR the code for this.

• /settings: add bluesky account, auth flow, disconnect flow, display username on profile
• @pushcx register a lobste.rs account for a bot
• @pushcx create a feed (roughly equivalent to a Twitter list, I think)
• Port script/mastodon_sync_list to sync to a feed
• Port script/mastodon_post_links to post front-page links
• @pushcx deploy scripts

[sknebel]

Bluesky currently doesn't have a good auth flow for third-party apps - there is a proposal to fix this: https://github.com/bluesky-social/proposals/blob/169b1932a802fa89602fb4a25e9221454403f951/0004-oauth/README.md

[pushcx]

Here’s a link to the current version of that, looks like it’s actively edited: https://github.com/bluesky-social/proposals/blob/main/0004-oauth/README.md