Repository-relative links open as https://<path> #760

Repository-relative links in a document, such as [review](docs/review.md), open as https://docs/review.md.

The dialect accepts these links (disguisedUrl only refuses relative paths that leave the repository), and the link editor offers "a path in this repository". But nothing resolves them against the document's repository:

• Lexical 0.48's LinkNode.createDOM sets href from sanitizeUrl, which calls formatUrl. formatUrl prefixes https:// to anything that doesn't start with a scheme, /, . or #, so docs/review.md becomes https://docs/review.md.
• follow in packages/editor/src/toolbar/link.tsx opens that href. A ./docs/review.md link would instead resolve against the Chopin page URL.

The Planner writes these links itself when it cites repository files, so most documents that reference code have broken links.

Expected: a repository-relative link opens https://github.com/{owner}/{repo}/blob/{default branch}/{path}, for example by overriding sanitizeUrl in a Chopin link node, or by resolving the path before it reaches Lexical.

Seen at e47b1a5. Changing the links through MCP update_document is also refused until the edited passages get new visuals, so the practical workaround is asking the Planner to use full GitHub URLs.