chore(whitepapers): fix the dead Ethereum whitepaper citation

[boleklebovski]

Problem

Reference [2] in content/foundations/whitepapers/ton.mdx cites the Ethereum whitepaper at https://github.com/ethereum/wiki/wiki/White-Paper. The ethereum/wiki repository has been deleted, so that URL returns 404 and the citation no longer resolves.

Change

One line. The citation now points at the whitepaper's current canonical home:

https://ethereum.org/en/whitepaper/ — HTTP 200, page title "Ethereum Whitepaper | ethereum.org".

Verification

• Old URL: 404. New URL: 200, and the page title matches the cited document.
• Control test: https://ethereum.org/en/bogus-path-zzz999/ returns a genuine 404, so a 200 from that host means the page really exists rather than a catch-all handler.
• No formatting risk. This file is excluded from all three of your format gates: .prettierignore lists *.mdx, .remarkignore lists content/foundations/whitepapers/ton.mdx explicitly, and the ignorePaths in .cspell.jsonc lists it too. So both check:fmt:some and the CSpell action skip it, and the change is a pure text substitution on one line — line count and every other byte are unchanged.

A second dead link I deliberately did not touch

Footnote 1 at line 2292 cites https://github.com/ethereum/wiki/wiki/Sharding-FAQ — also 404, from the same deleted repository. I left it as-is because I could not find a replacement I am able to vouch for, and I would rather flag it than quietly point the citation somewhere else:

• eth.wiki/sharding/Sharding-FAQs looks like the successor and returns HTTP 200 — but it is not the FAQ. That host is a blanket redirect: every path on it, including a deliberately bogus one I tested, lands on https://ethereum.org/ and returns a byte-identical 306,918-byte response. Checking only the status code would have made this look like a valid fix.
• github.com/ethereum/sharding is alive, but its docs/doc.md is the sharding specification, not the FAQ (it contains no occurrence of "FAQ"), and the repository has been archived since June 2018.
• ethereum.org/en/roadmap/danksharding/ is live, but it is a different document. Substituting it would silently change what the footnote cites.
• A Wayback snapshot would be the faithful fix, but archive.org rate-limited my requests and I am not willing to put in a URL I have not verified myself.

Since this is a footnote in a published whitepaper, which of those you want — or whether the URL should simply be dropped — is your call rather than mine. Happy to add it to this PR once you say which.

For context on why these survived: check:links in package.json is currently a placeholder (echo 'TODO: REPLACE mint broken-links ...'), so nothing in CI is validating external URLs at the moment.