docs(case-study): the subject package renamed axi-core -> axi-toolkit

Same package, new name. One mention, in the dateline; no URLs or identifiers
referenced it, so nothing else moves.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01NynrRND6ZUwGvq3ZUTCfxG

Author: dmealing

docs/case-study-requirements-first.md

@@ -1,6 +1,6 @@
 # Requirements-first with MetaObjects: a measured case study
 
-*2026-08-23. Written against `axi-core`, a new Python package, using the MetaObjects 0.24 line.*
+*2026-08-23. Written against `axi-toolkit`, a new Python package, using the MetaObjects 0.24 line.*
 
 This is a record of one thing that worked, with the numbers behind it and the boundary around
 it. It is deliberately specific: the interesting result is not "MetaObjects is good for