feat: move session sharing and collab rooms into a plugin (B12)

drizzle/sqlite/0037_burly_enchantress.sql

@@ -0,0 +1,6 @@
+-- session_shares, session_share_participants, collab_rooms and
+-- collab_room_members moved to the session-sharing plugin, whose first
+-- migration renames them. Dropping them here would lose every share and
+-- room, so this only stops drizzle tracking them. SELECT 1 because MySQL
+-- rejects an empty query.
+SELECT 1;