/trade-in/** is proxied by Caddy to a separate tradein-frontend app
(basePath /trade-in, canonical /trade-in/v2). The internal <Link
href="/trade-in/"> made Next prefetch an RSC payload for a route this
app doesn't own -> Caddy returns the other app's 307 -> 'Failed to fetch
RSC payload for /trade-in' + ChunkLoadError in the console on every
landing visit. Add NavItem.external; external items render a plain <a>
(no prefetch/client-nav) pointing at the canonical /trade-in/v2. Pilot
ACL unaffected: /trade-in/v2 still matches the /trade-in/** allow glob
(test added).
