chore(Hugo): deprecation warnings

The production build log contains the following deprecation info and warnings:

```
INFO deprecated: cascade._target was deprecated in Hugo v0.156.0 and will be removed in a future release. Use cascade.target instead, see https://gohugo.io/content-management/front-matter/#target
Start building sites …
hugo v0.157.0-7747abbb316b03c8f353fd3be62d5011fa883ee6+extended linux/amd64 BuildDate=2026-02-25T16:38:33Z VendorInfo=gohugoio

INFO build: step process substep collect files 4989 files_total 4989 pagesources_total 4989 resourcesources_total 0 duration 117.996417ms
INFO build: step process duration 118.069208ms
INFO static: syncing static files to / duration 464.264259ms
WARN deprecated: The "_build" front matter key was deprecated in Hugo 0.145.0 and will be removed in a future release. Use "build" instead. See https://gohugo.io/content-management/build-options.
INFO build: step assemble duration 1.381118453s
INFO deprecated: .Site.Data was deprecated in Hugo v0.156.0 and will be removed in a future release. Use hugo.Data instead.
```

Search the repository for the deprecated cascade._target, _build front matter, and .Site.Data usages named in the production build log. Run the production Hugo build to reproduce the warnings; done when those deprecation messages no longer appear.

Written by the indexing model from the issue text.