Configure the Fumadocs site so it can be served at multica.ai/docs:
- Add basePath: '/docs' to apps/docs/next.config.mjs
- Flatten routes: drop standalone home, render content/docs/index.mdx at
the root, move catch-all from app/docs/[[...slug]] to app/[...slug]
- Wrap children with DocsLayout in the root layout (was a separate
segment-level layout under app/docs/)
- Set source loader baseUrl to '/' so URL slugs no longer carry the
basePath (Next.js prepends it automatically)
- Strip the now-redundant '/docs/' prefix from internal MDX links and
drop the duplicate "Documentation" nav entry
- Add app/not-found.tsx for App Router 404 handling
Wire up multi-zone routing so apps/web proxies /docs/* to the docs app:
- Add DOCS_URL env (default http://localhost:4000) and rewrites for
/docs and /docs/:path* in apps/web/next.config.ts
- Whitelist DOCS_URL in turbo.json globalEnv
