Add case study: Corridor Dynamics in Coordinated Systems (Moore 2026)

A worked example of running the 6-step playbook on a real preprint
that is neither a clear win nor a clear failure. The artifact mixes a
shippable engineering anchor, a method-novel empirical layer, and a
speculative cosmological coda — with the author explicitly separating
the tiers and preregistering twenty falsification handles.

Shows what the kit does in the messy middle: situating, not
adjudicating. Names the relevant state of the art (edge of chaos,
SOC, active inference), steelmans neighbouring frameworks, and lets
the author's own tier separation carry the weight where it does.

Also adds essay/case-studies/README.md with an index and contributing
guidance for future cases.