Fix bootstrap script PEP 668 error and Python 3.14 compatibility

[Copilot]

CI failing on macOS runners due to PEP 668 blocking pip install virtualenv into system Python, and Python 3.14 requiring ansible-core >= 2.20.0.

Changes

• Replace virtualenv installation with built-in venv module in script/bootstrap
• Pin ansible-core>=2.20.0 in requirements.txt for Python 3.14 compatibility

# script/bootstrap
-python3 -m pip install virtualenv
-python3 -m virtualenv env
+python3 -m venv env

# requirements.txt
-ansible
+ansible-core>=2.20.0
 ansible-lint[yamllint]

The venv module is built-in since Python 3.3, no functional change to virtual environment behavior. Python 3.14 requires ansible-core >= 2.20.0, which needs to be pinned directly since the ansible metapackage (versions 12.x) still uses ansible-core 2.19.x.

<issue_title>Fix failing lint tests on main</issue_title>

<issue_description></issue_description>

Comments on the Issue (you are @copilot in this section)

Original prompt

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This section details on the original issue you should resolve

<issue_title>Fix failing lint tests on main</issue_title> <issue_description></issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes benbalter/dotfiles#47

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