Rewrite lexicon page copy in plain voice; render backtick spans as <code>
The owned-schema descriptions come from the lexicon JSON and were emitted as
plain text, so their Markdown backtick spans showed literally instead of as
<code>. Add a tested parseInlineCode helper that splits a description into
text/code segments; the page maps code segments to <code> and lets Astro escape
the rest (no raw HTML on the read path).
Also reword the hand-authored prose without em-dashes and drop the lone em-dash
in the lexicon's own description (single-sourced, so it shows on the page too).