Move the live GitHub stars widget into the sidebar footer pill as a
type:"icon" link, sitting opposite the Slack mark (space-between) and
beside the theme switcher. Render it as inner content (GitHub mark +
star + compact count) so fumadocs supplies the anchor.
Replace the default fumadocs theme switcher with a custom two-icon
control where each icon selects its own theme. The built-in
"light-dark" mode is a single blind toggle that flips on any click, so
clicking the sun while already in light mode jumps to dark. useTheme is
sourced from fumadocs-ui/provider/base and the icons are inlined to
avoid bare next-themes / lucide-react imports.
