feat: finish the ai plugin (B18)

drizzle/sqlite/0044_gorgeous_yellow_claw.sql

@@ -0,0 +1,6 @@
+-- The ai tables moved to the ai plugin, which renames them into its own
+-- namespace at activation, and ssh_data.enable_ai_assistant and the two
+-- user_preferences ai columns moved to its settings. Both run after this
+-- migration, so a real DROP here would delete the data first. The columns
+-- stay in place, unused, until 3.0.0.
+SELECT 1;