Converts content/gift/index.md to _index.md and extracts the shared
hero/form rendering into a partial (courses-body.html) used by both
single.html and a new list.html, so /gift renders identically but can
now hold real child pages like /gift/<partner>/.
The gift.reground.org vanity redirect already forwards any path
generically (redir https://reground.org/gift{uri}), so no
infrastructure change is needed to support future partnership URLs
like gift.reground.org/cheyenne once a matching page exists here.
will