docs(site): Fumadocs documentation site on TanStack Start

New standalone app at docs-site/ — Fumadocs (fumadocs-core/ui 16, fumadocs-mdx
15) on TanStack Start (Vite 7 + nitro-v2 bun preset, React 19, Tailwind 4),
mirroring the web/ console stack but with no auth/i18n/orval — docs stay public.

- catch-all docs route (routes/docs/$.tsx), Orama search (routes/api/search.ts),
  RootProvider shell, MDX component map, shared nav, custom 404
- content/docs/: hand-written index.mdx + meta.json nav, plus 7 pages imported
  from repo docs/ + README (leading H1 stripped, YAML frontmatter added; kept as
  .md so existing </{ don't trip MDX JSX). Content is a one-time snapshot.
- mdx() is plugins[0]; tsconfig collections/* -> ./.source/*; SSR search variant;
  @source for fumadocs-ui classes. Generated .source/routeTree/dist/.output ignored.

Verified: bun run build (client+SSR+nitro) green, tsc clean, dev + prod servers
serve all routes 200 with SSR content + nav, search returns hits, 404 works.

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

docs-site/src/routes/index.tsx

@@ -0,0 +1,26 @@
+import { createFileRoute, Link } from '@tanstack/react-router'
+import { HomeLayout } from 'fumadocs-ui/layouts/home'
+import { baseOptions } from '@/lib/layout.shared'
+
+export const Route = createFileRoute('/')({ component: Home })
+
+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>
+        <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.
+        </p>
+        <Link
+          to="/docs/$"
+          params={{ _splat: '' }}
+          className="rounded-lg bg-fd-primary px-5 py-2.5 font-medium text-fd-primary-foreground"
+        >
+          Read the docs
+        </Link>
+      </main>
+    </HomeLayout>
+  )
+}