Add ScramDB

[vertexclique]

This is a native submission, installed through the official installer pinned to one published build (c664e19).

Results:

• c6a.4xlarge (results/20260905): the reference run, 500 GB gp2.
• c7a.metal-48xl (results/20260906): the same scripts and build, unchanged, 500 GB gp2. On this machine the cold runs and the load are limited by a storage-engine defect on our side, not by the box: the engine keeps only about two I/O requests in flight on EBS, so cold reads and load writes wait on per-request latency (the volume never reached its IOPS or throughput ceiling; CloudWatch queue depth 1.7 to 4.3, burst balance 99 to 100). The hot column is representative of the engine on 192 vCPU; the cold and load columns will improve when the queue-depth fix ships, and the result will be re-run then.