Switch Twitter Bot to BlueSky bot

[jkomoros]

Rip out the twitter bot functionality and change it to a BlueSky API equivalent.

Ideally we'd keep the tweet counts for historical reasons but now update the blue sky counts, and the total counts would be the sum of all of them.

See also #686 for doing this for Threads.

[jkomoros]

• [ ] Verify that screenshot machinery still works
• [ ] BlueSky logo in the topbar
• [ ] Rename things like tweet-helper.ts et al to be social-helper.