Feature Request: Easily Add Folder to PYTHONPATH from VS Code UI

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Hi, I’m not sure if this belongs here or in [vscode-python](https://github.com/microsoft/vscode-python), but I’d like to request a more user-friendly way to add folders to the Python path in VS Code.

### Current Situation

- The `python.analysis.extraPaths` setting only affects IntelliSense, not the runtime `PYTHONPATH`.
- Using a `.env` file with `PYTHONPATH=path1;path2;path3` is unreliable (in my experience) and not user-friendly.
- **Creating a `.pth` file in `.venv/Lib/site-packages/` as below works, but is also tedious and not user-friendly.**
```
path1/src/
path2/src/
...
```

### Feature Proposal

It would be very helpful to have:
- A context menu command when right-clicking a folder (e.g., “Add to Python Path”)
- An accessible command in the Command Palette (`Ctrl+Shift+P`)
- A button in the python-environments extension UI (it would be very intuitive to have a small icon/button next to each venv in the list. Clicking this button could prompt the user to select a folder, and then automatically add that folder to the venv using the `.pth` method.)

This should add the folder to the Python path of the currently selected virtual environment in VS Code.

This would make managing the Python path much easier, especially for users coming from PyCharm, where this is a standard feature.

Thanks!

The issue names no files, tests, or implementation entry points; start by determining whether this belongs in vscode-python or vscode-python-environments and reviewing the existing environment UI and command registration. Done would require a decided scope and a user-facing way to add a selected folder to the currently selected virtual environment's Python path.

Written by the indexing model from the issue text.