A TTS voice browser embedded in the docs: a bordered list of two-line rows
(name over muted meta) with play-to-audition and copy-config, scoped under
.vw.vw-rows and following the docs' light/dark brand tokens.

- fern/components/voice-widget: the widget (index.tsx) over a shared data/helper
  engine (engine.tsx) + types; styles in styles.css. Loading state is a
  row-shaped skeleton built on the generic skeleton primitive.
- Registered via docs.yml experimental.mdx-components + css.
- Embedded on all 11 TTS pages (provider-locked on each provider page,
  groupBy="none" on the index).

Supersedes the earlier stacked PRs #392 (parent), #407 (card refinements), and
#409 (rows). The competing card design was dropped per the design decision to
ship the rows layout; only the rows widget and its self-contained stylesheet
remain.