Add simple Rust install deps

- teach `install` to plan and pour simple runtime
  dependency trees before linking the requested formula.
- cover the new path in `tests/cli.rs` and note the
  `aview` smoke test in `README.md` because
  `libaacs` still falls back to Ruby.
- record that `brew fetch aalib aview` was needed
  here while the Rust GHCR downloader still fails on
  uncached bottles.