Render table footnotes below their table

What does this MR do and why?

Goldmark's footnote extension is already enabled on the docs site, so [^1] renders a superscript link and a page-bottom endnotes block today. No page uses it, because footnotes referenced from a table land at the bottom of the page rather than the bottom of the table.

Our current process is that we use <sup>N</sup> plus a **Footnotes**: list. There is no link to the note, no link back, and the numbers are kept in sync by hand.

Findings

• No renderer work was needed for the superscript links. They already render.
• /help needs no change.
• Vale was a hard blocker. gitlab_docs.ReferenceLinks flagged every [^1]: text line as an error. Fixed. Syncing to the other content repos is a follow-up.
• scroll-margin-top cannot offset a reference inside a table. .table-container computes overflow-y: hidden (forced by overflow-x: auto), making it a scroll container that consumes the margin before the document scroll sees it. Without this, a return link lands the row behind the sticky table header. Fixed. The same offset is applied to deep links (#fn:N) that target a definition relocated below its table, and to deep links to a reference inside a table.
• The sticky header clone duplicated IDs from the source header, so fragment navigation could resolve to the hidden clone. Fixed.

Limitation

Footnotes inside shortcodes (tabs): Hugo renders shortcode inner content in a separate pass. A reference to a definition outside the shortcode renders as literal text; a definition inside restarts numbering at 1 and emits a second footnotes block, producing duplicate fn:1 IDs.

Suggestion: Update the style guide with something like this:

Do not use footnotes inside shortcodes

Follow-ups, not in this MR

• Sync the ReferenceLinks.yml fix to gitlab and charts/omnibus/runner/operator/cli.
• Rewrite the footnotes style guide section to document [^label]. Should land only after this deploys.
• locales/en-us.json gains a tables.footnotes string with no ja-jp counterpart. It falls back to English until the next translation push.

Related

• Related to #726 (closed)

Screenshots, screen recordings, or links to review app

Table footnotes

Light	Dark

Others

Deep link clears table header	Body text footnotes

How to set up and validate locally

1. Check out this branch.
2. Run yarn build then mise exec -- hugo serve -D.
3. Open http://localhost:1313/footnote-tests/.
4. Select a superscript marker, then the return link next to the definition.
5. Scroll until the sticky table header is showing, then use a return link and confirm the row is not hidden behind it.
6. Load http://localhost:1313/footnote-tests/#fnref:3 directly and confirm the same.
7. Load http://localhost:1313/footnote-tests/#fn:3 directly and confirm the relocated definition clears the sticky header. Goldmark numbers footnote IDs sequentially by first reference, so the [^runner] definition is fn:3. There is no fn:runner.
8. Confirm the two prose footnotes stay in the page-level block at the bottom.

Merge request acceptance checklist

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