Patch: backlinks + related under articles

Every article under thoughts/ and user/ should show two blocks under its body: backlinks (notes that link here) and related (semantically similar notes). Rather than add a content: list to each note, this patch sets it once.

It only applies when the note does not already declare its own content or widgets. That guard leaves the _index magazine pages (content: [self, magazine]) and the few user-doc pages with custom layouts untouched. Hidden _-prefixed notes (sidebars, index, headers) are excluded by the glob above, so sidebars and index listings are never rewritten.

The keywords match the sidebar widget vocabulary: self renders the note body, backlinks (alias of inlinks) the inbound-link list, similar the vector-similarity "related" list. Note that backlinks only shows something when other notes actually link here — a fresh essay with no inbound links renders an empty backlinks block; similar is content-based and works as soon as vector search is enabled.

See frontmatter-patches for the patch model and subgraphs for how a folder-scoped glob layers on top of the site-wide patches.

if std.objectHas(meta, "content") || std.objectHas(meta, "widgets")
then {}
else { content: ["self", "backlinks", "similar"] }