The README What's-new callout and the CHANGELOG 2.1.0 entry still said four number entities, while the README table/intro and the runtime-range-controls spec say five (the four range bounds plus ramp_half_width). Update the callout to list all five and add a CHANGELOG entry for the fifth entity; leave the historical 2.1.0 'four' entry intact. Docs only -- code and spec already reflect five. Filed as openspec change fix-number-entity-count-docs.
