Migrate from Poetry to uv, bump Python to >=3.11

[astanziola]

Summary

• Migrate build system from Poetry to uv (hatchling backend)
• Bump minimum Python to 3.11 (plumkdocs 1.0.0 requires it)
• Upgrade plumkdocs to >=1.0.0, mkdocstrings to >=1.0.0
• Drop transitive dev deps already pulled by plumkdocs (griffe, mkdocs-material, mkdocs-macros-plugin, mkdocstrings, mkdocstrings-python)
• Update all CI workflows to use uv run instead of poetry run
• Update GitHub Actions to latest versions (checkout@v4, setup-python@v5, codecov@v5, etc.)
• Add uv.lock

Supersedes #244.