logo.svg was 56KB of unminified, high-precision path data with no
embedded raster. Running it through SVGO (default preset, multipass)
cuts it to ~20KB with no visual difference.
perf(docs-site): further minify header logo SVG. Cut to ~8.9KB with no visual difference.
The header social link used Starlight's generic `code-branch` icon.
Wires up starlight-plugin-icons + UnoCSS (Iconify) and overrides
SocialIcons to render `pajamas:gitea` for the Gitea link instead, while
falling back to Starlight's default icon set for anything else. Sidebar
and codeblock icon support are enabled but unused for now.