docs(plans): record Step 2 as one behavioral test file

Step 2 (!2719 (merged)) shipped without the rowshapes mirror and the enumerated kind/format/visibility sweep the plan booked: structure.sql pins the catalog byte-for-byte, the foreign key reads none of those columns, and the container junction's suite drops the sweep for the same reason. The Files and Tests bullets and the size estimate now say what the step delivers, including the static file-shape checks the testing guide asks for.

Requested in the review of !2719 (merged) (the plan is the contract, so the trim needs the plan to say so).

Related to #289