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/docs/$.tsx

@@ -0,0 +1,58 @@
+import { createFileRoute, notFound } from '@tanstack/react-router'
+import { DocsLayout } from 'fumadocs-ui/layouts/docs'
+import { createServerFn } from '@tanstack/react-start'
+import { source } from '@/lib/source'
+import browserCollections from 'collections/browser'
+import { DocsBody, DocsDescription, DocsPage, DocsTitle } from 'fumadocs-ui/layouts/docs/page'
+import { baseOptions } from '@/lib/layout.shared'
+import { useFumadocsLoader } from 'fumadocs-core/source/client'
+import { Suspense } from 'react'
+import { useMDXComponents } from '@/components/mdx'
+
+export const Route = createFileRoute('/docs/$')({
+  component: Page,
+  loader: async ({ params }) => {
+    const slugs = params._splat?.split('/') ?? []
+    const data = await serverLoader({ data: slugs })
+    await clientLoader.preload(data.path)
+    return data
+  },
+})
+
+const serverLoader = createServerFn({
+  method: 'GET',
+})
+  .validator((slugs: string[]) => slugs)
+  .handler(async ({ data: slugs }) => {
+    const page = source.getPage(slugs)
+    if (!page) throw notFound()
+
+    return {
+      path: page.path,
+      pageTree: await source.serializePageTree(source.getPageTree()),
+    }
+  })
+
+const clientLoader = browserCollections.docs.createClientLoader({
+  component({ toc, frontmatter, default: MDX }, _props: undefined) {
+    return (
+      <DocsPage toc={toc}>
+        <DocsTitle>{frontmatter.title}</DocsTitle>
+        <DocsDescription>{frontmatter.description}</DocsDescription>
+        <DocsBody>
+          <MDX components={useMDXComponents()} />
+        </DocsBody>
+      </DocsPage>
+    )
+  },
+})
+
+function Page() {
+  const data = useFumadocsLoader(Route.useLoaderData())
+
+  return (
+    <DocsLayout {...baseOptions()} tree={data.pageTree}>
+      <Suspense>{clientLoader.useContent(data.path)}</Suspense>
+    </DocsLayout>
+  )
+}