feat(migrate): support Python migrations from uv

[CalvinAllen]

Summary

Add support for migrating Python installations managed by uv to dtvem.

Background

uv is a fast Python package and project manager from Astral (makers of Ruff). It can manage Python versions similar to pyenv, and is gaining popularity.

Requirements

• Detect uv-managed Python installations
• Detect and preserve global packages installed via uv
• Support migration of uv Python versions to dtvem

Implementation Notes

• uv stores Python installations in ~/.local/share/uv/python/ (Unix) or similar on Windows
• Need to create a new migration provider at src/migrations/python/uv/provider.go
• Follow the pattern established by the pyenv migration provider

References

• uv documentation
• uv Python management