fix installer path: use XDG base dir instead of Cargo

[ShotaArima]

When I was using Docker for uv, I encountered the following error

$ docker compose up --build

 => ERROR [app 6/6] RUN . $HOME/.bashrc && uv sync                                                                                0.2s
------                                                                                                                                 
 > [app 6/6] RUN . $HOME/.bashrc && uv sync:
0.121 /bin/sh: 21: .: cannot open /root/.cargo/env: No such file
------
failed to solve: process "/bin/sh -c . $HOME/.bashrc && uv sync" did not complete successfully: exit code: 2

This was due to a change in uv Pull Request #8420

In this change, environment variables that depended on Cargo are now XDG compliant.

[shunsock]

Thank you for your contribution. I've checked my environment, and the issue is reproducible.