Docusaurus migration: custom-styled blocks

On the 11ty-based site, we have some custom code blocks:

* admonitions (only one type, `info` -- it'd be nicer if we had the usual full palette of admonitions such as `warn` and `tip`)
* `intro`
* `orientation`
* `storystep`
* `h-author` (not sure what this is for; check to see whether it's still needed)
* `topic-list`
* `output-block` (made to suppress the copy button on code blocks)

Replicate their functionality and, if necessary, change Markdown documents to match whatever syntax they now use.

Start by locating the existing 11ty custom block definitions and searching the Markdown documents for admonitions, intro, orientation, storystep, h-author, topic-list, and output-block usage. Map each block to the Docusaurus syntax, verify whether h-author is still needed, and confirm that the affected documentation renders with equivalent behavior.

Written by the indexing model from the issue text.