webui: fix syntax highlighting lost after streaming for non-common languages (#21206)

webui: fix syntax highlighting lost after streaming for non-common languages (#21206)

* webui: fix syntax highlighting lost for non-common languages after streaming

rehype-highlight uses lowlight internally, which only bundles 37 "common"
languages. The streaming code path uses highlight.js directly (192 languages),
so languages like Haskell highlight correctly while streaming but lose all
color once the code block closes. Pass the full lowlight language set to
rehype-highlight so both paths support the same languages.

* webui: rebuild static files after rebase