/**
* Emits + for the media CDN
* domain (R2_PUBLIC_URL), so the browser opens the TLS/DNS connection to the
* media host early — before it hits the first . Saves ~150–300ms on the
* first image load.
*
* Reads the domain from R2_PUBLIC_URL (the same env var buildR2Storage uses),
* so there's ONE source of truth — no per-project hardcoded domain. Renders
* nothing when R2_PUBLIC_URL isn't set (local disk / no CDN → nothing to
* preconnect).
*
* Server Component — drop it in the