feat: enhance limits

migrations/0042_user_limit_overrides.down.sql

@@ -0,0 +1,5 @@
+ALTER TABLE users DROP CONSTRAINT IF EXISTS users_limit_overrides_nonneg;
+ALTER TABLE users
+    DROP COLUMN IF EXISTS bookmark_limit,
+    DROP COLUMN IF EXISTS public_collection_limit,
+    DROP COLUMN IF EXISTS private_collection_limit;