Update virtual environment name in documentation from venv to .venv

[Aevarkan]

Note that this updates .gitignore in addition to documentation pages.

This PR changes a few things regarding the documentation for installation:

• updates the virtual environment's name to .venv from venv to align it with uv's functionality.
• separate the Windows tab into Command Prompt and PowerShell (see here for the command syntax used)
• update the .gitignore file to exclude the virtual environment

This is what the updated version looks like:

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This is what the old version looks like:

[Aevarkan]

I saw that Tutorials > Install your plugin also had venv:

• Made another commit 10ab08b that changes it to .venv
• Also split Windows to Command Prompt and PowerShell to align it with Getting Started > Contributing.

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Also made 7dc05fe to fix this message that appeared during documentation deployment:

INFO    -  Doc file 'tutorials/install-your-plugin.md' contains an unrecognized relative link '../../getting-started/installation/#environment', it was left as is. Did you mean '../getting-started/installation.md#environment'?

[Aevarkan]

I did just look at #226. I believe that it'll be fine if there's a divergence there (that PR uses .virtualenvs), as start.sh and autoinstall.sh are used for production, not development.

This PR regards documentation on the manual development side, so I don't believe the scopes overlap.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 0.00%. Comparing base (37f8527) to head (7dc05fe).
⚠️ Report is 2 commits behind head on main.

Additional details and impacted files

@@     Coverage Diff     @@
##   main   #383   +/-   ##
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