chore: rename repo's own CONTEXT.md to GLOSSARY.md

This is the skills repo's own domain glossary, not the CONTEXT.md
convention that skills like domain-modeling and grill-with-docs read
and write in consumer repos — that convention is left untouched.

Co-Authored-By: Claude <noreply@anthropic.com>

.changeset/rename-context-to-glossary.md

@@ -0,0 +1,5 @@
+---
+"mattpocock-skills": minor
+---
+
+Rename this repo's own root domain glossary from `CONTEXT.md` to `GLOSSARY.md`. This only affects the skills repo's own file — the `CONTEXT.md` convention that skills like `domain-modeling` and `grill-with-docs` read and write in consumer repos is unchanged.