rootful is broken

If you use the python copier template developer container and you have docker (or rootful podman) then it does not work as intended:

- GOOD: it loads and you can work on the project and run tests
- BAD: massively insecure as you are running as true root
- UGLY: project files get written by root and the git gets really angry

There used to be a workaround to this in devcontainer.json
```json
"remoteUser": "${localEnv:VSCODE_REMOTE_USER}"
```

docker users were then expected to set VSCODE_REMOTE_USER=$(id -u):$(id -g) in their bashrc.
podman users need do nothing as blank == default == root which is just right in a a rootless container.

Not ideal. But it was the best I could come up with.

Start with the devcontainer.json configuration in the Python Copier template and reproduce the behavior using Docker or rootful Podman. Compare the current container user handling with the former VSCODE_REMOTE_USER workaround; done should mean the container remains usable without running as true root or leaving project files owned by root.

索引モデルが issue の本文から書いたものです。