Add setup check command and include bats-core in base install

[codeforester]

Summary

This PR polishes the initial setup.sh command before moving on to the Python CLI setup work.

The setup command now installs the full base toolchain we need for this repo, including bats-core, and adds a read-only check subcommand for validating whether the local CLI environment is ready.

What Changed

• added bats-core to the base setup.sh install flow
• kept BATS installation idempotent via brew list bats-core
• added dry-run logging for BATS installation
• added BANYAN_SETUP_BATS_FORMULA override for tests/automation
• added setup.sh check as a read-only environment validation command
• made check verify:
  • Homebrew
  • Xcode Command Line Tools
  • Python python@3.13
  • BATS bats-core
  • $HOME/.banyanlabs.d/.venv
• made check exit 0 when everything is present and 1 when anything is missing
• updated setup docs and help text
• expanded BATS coverage for BATS install behavior and both passing/failing check paths

Testing

Validated with:

bats cli/env/tests/banyanenv.bats cli/bash/bin/tests/bash-wrapper.bats cli/bash/commands/setup/tests/setup.bats