fix(docs): align MODULE-SYSTEM-PROGRESS with main to clear #614 merge conflict

#615 was squash-merged, which carried main's content into the feature
branch but not its ancestry, so #614's 3-way merge re-derived a
modify/delete conflict on docs/history/MODULE-SYSTEM-PROGRESS (main
modified the .md in #602; this branch had migrated it to .adoc).

Resolve squash-robustly by matching main exactly for this file: restore
main's .md and drop the .adoc. No content is lost — main's .md already
carries the #138 codegen-follow-up note. The .md->.adoc migration can be
redone later as a standalone DOC-FORMAT change.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Lz7pRcec2Z3tVtaAhvB3M8

Author: claude