docs(readme): convert README.adoc -> real Markdown (fix raw-asciidoc render on Glama/community-health) (#260)

**Fixes the raw-AsciiDoc rendering** on
https://glama.ai/mcp/servers/hyperpolymath/boj-server (and GitHub
community-health). The README was AsciiDoc (`README.adoc` + a
`README.md` carrying raw asciidoc syntax) → consumers that render
Markdown show literal `= boj-server`, `:toc:`, `[source,bash]`,
`image:[]`, `link:[]`. Converts the source to GFM via pandoc (badges →
clickable `[![alt](src)](link)`), keeps the CC-BY-SA-4.0 SPDX header as
an HTML comment, removes the duplicate `README.adoc`. Count (115)
carried verbatim; the 115/125/139 reconciliation is separate (#256).

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

Author: hyperpolymath