Fix generated documentation rendering

[LukasNiessen]

Summary

• use Kramdown-compatible fenced code blocks throughout the README
• prevent literal fence markers and wildcard emphasis from leaking into generated docs

Verification

• bundle exec rake docs (169 pages and internal links validated)
• bundle exec rake (455 examples, 0 failures; RuboCop 235 files, no offenses)

[TristanKruse]

Reviewed the README fence conversion. The guide renders 26 code blocks with syntax highlighting and no literal fence markers. Existing CI passes; code examples are preserved.