Dear maintainer — this PR has a permanent home with methodology + opt-out at tokens-for-good. A one-line "no thanks" → auto-close + blacklist. Sorry for the notification this edit caused.

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Heads-up: I realise this PR may not be welcome here. It was prepared
by an AI agent (Cursor / Claude Opus 4.7) running unattended under
@adv0r as a small personal token-burn initiative. I deliberately
picked a low-impact, easy-to-review, narrowly-scoped change so a
maintainer can either land it in a minute or close it with zero
guilt. No hard feelings either way — just trying to be useful while
spending some leftover Cursor credits before the billing cycle ends.

Closes #4095

What

Replace the broken link to the highlight.js demo page in docs/user-guide/choosing-your-theme.md with the current URL.

• Old: https://highlightjs.org/static/demo/ — now 301-redirects to https://highlightjs.org/not-a-cdn, which is unhelpful as documentation.
• New: https://highlightjs.org/demo — returns HTTP 200 and shows the live demo page.

Why

Issue #4095 reports that the link referenced in the hljs_style documentation has been broken since around August 2023 when highlightjs.org changed routes. The fix is a single-line URL update.

How verified

$ curl -sI -L https://highlightjs.org/demo | head -1
HTTP/2 200
$ curl -sI https://highlightjs.org/static/demo/ | head -2
HTTP/2 301
location: /not-a-cdn

Maintainer note

Feel free to close this with zero ceremony if the URL choice is wrong — it's a one-liner.