Fixes#294
## Summary
- detect missing desktop Node runtimes before spawning the bundled CLI
- return a clear error message that tells users to install Node.js or
set `NODE_BINARY`
- handle both direct spawns and desktop-shell launches consistently
## Validation
- `npm run bundle:server --workspace @codenomad/tauri-app && cargo build
--manifest-path packages/tauri-app/src-tauri/Cargo.toml`
- exercised the missing-runtime path in the Linux VM by launching with
an invalid `NODE_BINARY`
e28e9f5879