Next.js 16 nests standalone output under the project directory name
when NEXT_TRACING_ROOT_MODE=workspace (e.g. standalone/9router/server.js
instead of standalone/server.js), causing build-cli.js to fail with
"Next.js standalone build not found".
Detect nested layout with backward-compatible fallback to existing
standalone/server.js and standalone/app/ paths.
Co-authored-by: Cursor <cursoragent@cursor.com>
