[DEMO] Add .venv/ and env/ to .gitignore #64

This is a demonstration issue. It is deliberately tiny, so it can be
done start to finish in a couple of minutes. If you are brand new, these are
the ones to start with.

Context

.gitignore covers __pycache__ and node_modules but not Python virtual environments. Anybody who makes a venv inside the project folder will see hundreds of files appear in git status, which is alarming the first time and leads to accidentally committing the lot.

What to change

Files: .gitignore

Requirements:

• Add .venv/ and env/ under the existing # Python heading
• Keep the existing grouping and comments — do not reorder the file
• One entry per line, matching the style already there

Acceptance criteria

• Both entries are present under the Python section
• The rest of the file is unchanged
• Creating a venv in the project folder no longer shows up in git status

How to verify locally

python3 -m venv .venv
git status          # .venv should not be listed
rm -rf .venv

How long this takes

One minute. Two lines. The smallest real contribution on the list.

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