docs(readme): convert README.adoc -> Markdown (renders on Glama/profile/community-health) (#20)

README was AsciiDoc → renders as raw markup in Markdown consumers (Glama
MCP directory, GitHub community-health, GitHub profile). pandoc
asciidoc→GFM (badges → clickable), SPDX header kept, duplicate `.adoc`
removed. Part of the estate README-format fix.

Co-authored-by: Claude Opus 4.8 <noreply@anthropic.com>

Author: hyperpolymath