Staircase 0.1.31

Three previews after 0.1.30: emoji pack discovery, the 8 MB attachment cap
removed in favour of your Blossom server's own limit (with a pre-flight ask, a
named refusal and an out-of-memory send that fails like any other), and hover
actions for a mouse on the web and the desktop app. Schema 23.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>