Add commands to manage Python PATH

[kipavy]

🚧 DRAFT POC - AI Generated Code 🚧

GitHub Copilot generated most of this code. Looking for feedback on approach.

What it adds

Two new commands for managing Python PATH:

• Add folders to Python PATH (creates .pth files)
• Open Python PATH file for editing

Where to find them

• Command palette: "Python: Add Folder to Python PATH"
• Right-click folders in Explorer
• Right-click environments in Python view
• Hovering on venvs in extension menu

How it works

• Finds site-packages using Python's own modules
• Creates vscode_extra_paths.pth files

Closes #735

First VS Code extension attempt - generated code for testing feasibility

[kipavy]

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[eleanorjboyd]

going to wait for community feedback on the issue before reviewing this PR as the issue will determine what exactly we need to add feature-wise