Context

Various environments run different versions of uv, so CI and local results are not reproducible, and a host's uv can be too old for the features the tooling relies on.

Definition of done

• A single known uv version is used by local dev (`just install`), Evergreen CI, and GitHub Actions.
• The version is defined in one place and bumped manually when a newer uv is needed.
• The pinned uv installs on Linux, macOS, and Windows without clobbering the toolchain or the running executable.

Pitfalls

• On Windows, native `uv.exe` needs Windows-form paths (cygwin paths are ignored), and `uv tool install` cannot overwrite the executable in use, so avoid copying uv to a temp location.
• The version lives in `[tool.uv] required-version` in `pyproject.toml`; Dependabot must not auto-bump it (updates are manual).