- Add `scripts/install.sh` — a single `curl | bash` installer that handles system deps, Rust, clone, build, and install
automatically.
- Update README Linux/macOS section with a "One-Line Installer (Recommended)" block above the existing manual steps.
1. Detects OS (Linux apt/dnf, macOS Xcode CLT)
2. Installs build deps + git via system package manager (sudo only here)
3. Installs Rust via rustup (skipped if already present)
4. Shallow-clones the repo to `/tmp/zeroclaw-install`
5. `cargo build --release --locked` + `cargo install --path . --force --locked`
6. Cleans up temp dir and prints next steps (`source ~/.cargo/env`, `zeroclaw onboard`)
