Move banyanenv to cli/env and wire bash-wrapper to shared CLI bootstrap

[codeforester]

Summary

This PR moves the shared CLI environment bootstrap out of cli/bash/ and into cli/env/, which is a better long-term home now that the environment contract is shared across Bash CLIs, Python CLIs, and interactive user shells.

It also updates bash-wrapper to consume the new shared bootstrap location and adds dedicated docs and tests for the environment layer.

What Changed

• moved banyanenv.sh from cli/bash/ to cli/env/banyanenv.sh
• added cli/env/README.md to document the shared CLI environment contract
• added cli/env/tests/banyanenv.bats for Bash and zsh coverage
• updated cli/bash/bin/bash-wrapper to source cli/env/banyanenv.sh
• updated wrapper docs and tests to reflect the new location and env metadata
• renamed the wrapper-facing env reference to BANYAN_CLI_ENV_SCRIPT to make the ownership CLI-wide rather than Bash-specific

Why This Structure

cli/env/ is a better fit than cli/bash/ because this bootstrap is no longer just a Bash implementation detail. It defines shared environment variables and PATH setup that affect:

• Bash command dispatch through bash-wrapper
• future Python CLI tooling
• user shell startup via ~/.bashrc or ~/.zshrc

This keeps the CLI environment layer separate from Bash-specific implementation code.

Testing

Validated with:

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