Set $VISUAL whenever $EDITOR is set

[rolandwalker]

Description

Set $VISUAL whenever $EDITOR is set, since prompt_toolkit consults $VISUAL first for the \edit command.

https://github.com/prompt-toolkit/python-prompt-toolkit/blob/c7c629c38b22b5f22a0a5e80a1ae7e758ac595bb/src/prompt_toolkit/buffer.py#L1626

Checklist

• I added this contribution to the changelog.md file.
• I added my name to the AUTHORS file (or it's already there).
• To lint and format the code, I ran

  uv run ruff check && uv run ruff format && uv run mypy --install-types .

[github-actions]

1. Behavioral mismatch: feature not implemented in runtime code
   The PR title/body and changelog claim “Set $VISUAL whenever $EDITOR is set,” but the only functional change is in test setup (before_all) and does not affect actual mycli runtime behavior.

• Changed line: test/features/environment.py:34
• Claim line: changelog.md:6
  Action: either (a) implement this in application startup/runtime env handling, or (b) adjust title/body/changelog to clarify this is test-environment-only.

No security issues found in the diff.

Testing gap:

• If runtime behavior is intended, add a test that verifies when only EDITOR is set, \edit still uses it even when VISUAL is unset/mis-set (unit/integration around editor invocation path).
• I couldn’t run tests in this environment because pytest/uv are not installed.