v0.1.0-rc.4

rc.3 attached six of eight files: the extension build could not resolve
onnxruntime-web from the CI job's install. Fixed, so this tag carries the
Chrome and Firefox zips as well as the desktop installers.

Contents as rc.3: the site now ships in eight languages -- 32 real
documents translated at build time, with hreflang, per-locale canonicals
and a sitemap listing all of them -- plus /styles, the preset gallery
rendered from the engine's own numbers, VAD before the recogniser,
inline-echo trimming, flicker merging in the Rust cue segmenter, and
language-label smoothing.