chore: delete duplicate .md docs superseded by canonical .adoc (Item 11)

Estate convention: AsciiDoc (.adoc) is the canonical doc format (RSR
template). These .md files are stale duplicates of an existing .adoc
sibling in the same directory — removed to end doc-drift.

Deleted: CHANGELOG.md

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

Author: hyperpolymath