Add a separate script that generates a large amount of fake elements for testing scalability. **Done when:** - [ ] The script adds 50,000–100,000 elements with `SYN-` ids in their own element groups - [ ] One command removes all synthetic data again - [ ] It is never run by the normal seed - [ ] `EXPLAIN ANALYZE` on the synthetic catalog shows that the search indexes are used, that a page far into the result is as fast as the first, and that a one-letter search returns in reasonable time - [ ] Search and filter times with and without indexes are measured and written in the README