fix: migration to properly drop unique index on friendly_name

The migration was dropping the constraint but not the underlying unique index.
In PostgreSQL, unique constraints and unique indexes can exist independently.
This caused auto-enrollment to fail with 'unique constraint violated' errors.

Added explicit DROP INDEX statement to ensure the unique index is removed,
allowing duplicate friendly_name values while machine_id remains unique.

backend/prisma/migrations/20251004090459_add_machine_id_to_hosts/migration.sql

@@ -7,6 +7,9 @@ UPDATE "hosts" SET "machine_id" = 'migrated-' || "api_id" WHERE "machine_id" IS
 -- Remove the unique constraint from friendly_name
 ALTER TABLE "hosts" DROP CONSTRAINT IF EXISTS "hosts_friendly_name_key";
 
+-- Also drop the unique index if it exists (constraint and index can exist separately)
+DROP INDEX IF EXISTS "hosts_friendly_name_key";
+
 -- Now make machine_id NOT NULL and add unique constraint
 ALTER TABLE "hosts" ALTER COLUMN "machine_id" SET NOT NULL;
 ALTER TABLE "hosts" ADD CONSTRAINT "hosts_machine_id_key" UNIQUE ("machine_id");