docs: plainer prose in README, guides, ADRs and context files

[lesnik512]

Edits prose only, to remove patterns that read as machine-written. Nothing about behaviour changes.

• Em dashes are replaced with colons, commas, parentheses or full stops.
• The README "intentionally differ" list loses its bold labels. The long extras bullet is split, and free-threading gets its own item.
• The quickstart "What you get" list drops its bold labels and dashes.
• ADRs and CONTEXT.md drop filler ("genuinely", "rather than a smell") and some contrasts that only added emphasis. Glossary _Avoid_: lines read as sentences.

Code blocks, inline code, link targets and every number and identifier are unchanged; a script compared them old against new. One dash remains, inside a code comment in the quickstart. The emoji headings at the end of the README match the other org repos and are left alone.

Checked with just docs-build (mkdocs build --strict).