feat(docs-site): brand the docs to match the punktfunk website

Theme the Fumadocs docs site with the punktfunk identity, mirroring the
marketing site:

- Swap the stock `neutral` preset for `purple`, then override --color-fd-*
  with the violet lens-mark palette (#6c5bf3 / #a79ff8). The brand is the
  violet, not the site's blue marketing background, so the blue is not used
  as a reading surface; dark mode tints the chrome toward the app-icon
  violet-dark (#1c1530).
- Adopt @unom/ui's token contract (--brand/--primary/--accent + bg-brand
  etc.) as the shared token source, and @source its dist.
- Load Geist (the brand typeface) via @fontsource-variable/geist.
- Add the BrandMark lens to the nav + landing hero, wire the brand
  favicon.svg, and add Docs/Website nav links.
- Keep the Fumadocs light/dark toggle.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

docs-site/src/routes/__root.tsx

@@ -2,6 +2,7 @@
 import { createRootRoute, HeadContent, Outlet, Scripts } from '@tanstack/react-router'
 import * as React from 'react'
 import { RootProvider } from 'fumadocs-ui/provider/tanstack'
+import '@fontsource-variable/geist'
 import appCss from '@/styles/app.css?url'
 
 export const Route = createRootRoute({
@@ -12,7 +13,10 @@ export const Route = createRootRoute({
       { name: 'color-scheme', content: 'dark light' },
       { title: 'punktfunk docs' },
     ],
-    links: [{ rel: 'stylesheet', href: appCss }],
+    links: [
+      { rel: 'stylesheet', href: appCss },
+      { rel: 'icon', type: 'image/svg+xml', href: '/favicon.svg' },
+    ],
   }),
   component: RootComponent,
 })

docs-site/src/routes/index.tsx

@@ -1,5 +1,6 @@
 import { createFileRoute, Link } from '@tanstack/react-router'
 import { HomeLayout } from 'fumadocs-ui/layouts/home'
+import BrandMark from '@/components/BrandMark'
 import { baseOptions } from '@/lib/layout.shared'
 
 export const Route = createFileRoute('/')({ component: Home })
@@ -8,15 +9,16 @@ function Home() {
   return (
     <HomeLayout {...baseOptions()}>
       <main className="flex flex-1 flex-col items-center justify-center gap-6 px-4 py-24 text-center">
-        <h1 className="text-4xl font-bold tracking-tight">punktfunk</h1>
+        <BrandMark className="size-20 drop-shadow-[0_8px_30px_rgba(108,91,243,0.45)]" />
+        <h1 className="font-display text-4xl font-bold tracking-tight">punktfunk</h1>
         <p className="max-w-xl text-fd-muted-foreground">
-          A ground-up low-latency desktop and game streaming stack, built Linux-first, with a
-          shared Rust protocol core and native clients per platform.
+          Linux-first, low-latency desktop and game streaming — a shared Rust protocol
+          core with native clients per platform.
         </p>
         <Link
           to="/docs/$"
           params={{ _splat: '' }}
-          className="rounded-lg bg-fd-primary px-5 py-2.5 font-medium text-fd-primary-foreground"
+          className="rounded-lg bg-brand px-5 py-2.5 font-medium text-white transition-colors hover:bg-brand/90"
         >
           Read the docs
         </Link>