Keep legacy subscription tables as unmanaged instead of dropping them

prisma.config.ts

@@ -5,6 +5,15 @@ import { defineConfig } from 'prisma/config';
 
 export default defineConfig({
 	schema: 'prisma/schema.prisma',
+	// Legacy subscription tables are retained in the database but are no longer
+	// managed by Prisma Migrate. They must never be dropped (production may not
+	// own them and the data is kept for recovery).
+	experimental: {
+		externalTables: true
+	},
+	tables: {
+		external: ['public.SubscriptionLevel', 'public.ProclamationCategorySubscriptionLevel']
+	},
 	migrations: {
 		path: 'prisma/migrations',
 		seed: 'tsx prisma/seed.ts'