Model `[[wikilinks]]` and `![[transclusions]]` as distinct inline node
types sharing a `{ target, anchor?, display? }` shape, and render them:
wikilinks underlined (display text or target), transclusions as their
raw source text.
remark-wiki-link is added to the pipeline for `[[…]]`. It does not
recognise `![[…]]` embeds or split the `#anchor` from the target, so
transclusions are recovered by scanning text runs and anchors are split
in the translation layer. Its alias divider is set to `|` so Step
Reference anchors like `#rolling:2` survive.
