Moves the MST inversion report out of the repo root into docs/, updating the 0.3.19 changelog entry that references it by path. Rewrites "used by" around what zat actually runs now. The list had grown by accretion and led with small consumers while omitting the ones that make the case: a PDS, a relay, and a Jetstream V2 service with the whole network archived behind it. Splits protocol infrastructure from applications, drops the weaker entries rather than appending to them, and fixes zlay's link — it lives at zat.dev/zlay, not zzstoatzz.io/zlay. Every URL and live endpoint in the new list was checked. Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>