Adds the discoverability-registry surface for issue #2182: JSON-sourced
capability/eos catalogs, a pure schema/vocab module (registry-schema.cjs)
with the ADR-857 loop points + ADR-1239 axes, thin validate/gen CLIs,
the registry-entry PR template, README spec, and CONTEXT.md glossary terms.
The three pure functions (isValidGsdRange/validateEntries/renderMarkdown)
are stubbed here so the comprehensive test suite fails first (red), per the
feature-implementation red-first directive; the next commit implements them.
Refs #2182
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
