measure: extend the catalog sample beyond three marketplaces

[jothimani-rajendran]

paper/measurements/catalog-sample/ holds statements for 18 public Claude Code plugins drawn
from three marketplaces: the official one, othmanadi-planning-with-files, and wshobson-agents.
Each is a real third-party artifact measured at a pinned commit.

Three marketplaces is a sample, not a survey. Extending it is among the most directly useful
contributions to this repo, and it needs no new code — just running the producer and adding what
it wrote.

What to do: pick a public Claude Code plugin marketplace not already in inventory.json,
measure its plugins with the reference producer at a pinned commit, and add the statements plus
the inventory rows.

The rules this sample is built under, from its own README, and they are not optional:

• Every artifact is measured as published — never authored, modified, or influenced by this
  repository or its maintainers.
• No plugin author is contacted. Nothing here is a request, a report, or a claim sent to them.
• Every statement is bound by digest to the directory it measured. A statement whose digest no
  longer matches a re-clone describes history, not the plugin's current state — say so rather than
  silently re-pinning.

Read paper/measurements/catalog-sample/README.md and SUMMARY.md before starting. SUMMARY.md
is the selection rule; follow it rather than picking plugins you like, or the sample stops being
one.

Sized to an afternoon per marketplace. No code required.