docs: drop dashes and bold labels from the site, profile and repo docs

[lesnik512]

A prose pass to remove AI-writing tells from docs/index.md, profile/README.md, README.md, CONTRIBUTING.md, brand/README.md, CONTEXT.md and AGENTS.md. No facts, repo names, links, tables or code changed.

• Mid-sentence em dashes are now colons, commas, semicolons or separate sentences. The hero line is edited the same way on the site and the profile, so the two still match.
• Bold-label bullets are plain: "The stack" on the site, "Ways to contribute", and the README.md list, which is now a short paragraph. The profile's "Which one?" label is gone; the sentence after it already says which one.
• CONTEXT.md: the _Avoid_: lines use a period or parentheses in place of the dash. Glossary terms stay bold.
• Emphasis bold inside sentences is removed in brand/README.md, CONTEXT.md and AGENTS.md.

Deliberately unchanged: docs/DEPLOYMENT.md (arrows), the bold card titles in the site's grid (Material card markup), the **cream** table cell in brand/README.md, the "~70–80%" range, and files outside this pass (docs/standard.md, SUPPORT.md, SECURITY.md, CODE_OF_CONDUCT.md, the ADRs).

uv run pytest passes (175 tests, including the profile/site listing invariants) and mkdocs build --strict is clean.