feat: unify alerts into one plugin, channels, rules and inbox

drizzle/sqlite/0054_superb_guardian.sql

@@ -0,0 +1,6 @@
+-- dismissed_alerts and notification_channels moved to the alerts plugin. It
+-- renames the first into its own namespace and copies the second at
+-- activation, both after this migration, so a real DROP TABLE here would
+-- delete them first. notification_channels stays in place, unused, until
+-- 3.0.0.
+SELECT 1;