Add support for importing local mcworld files

- Specified by user by an environment variable such as `IMPORT_MCWORLD`
- Would be a **container** path to the file
- Docs could suggest mounting a host directory to a container path such as `/worlds`
- Contents of mcworld would be unzipped. If the resulting level directory already exists, skip the rest with a logged warning.
- Identifies level name
- Sets level name environment variable to be provided to properties file management

Start by tracing the environment-variable handling and properties-file management entry points, then identify where world initialization and logging occur. Verify the requested container-path import, archive extraction, existing-level warning, level-name detection, and environment-variable handoff; update the documentation to describe mounting a host directory such as /worlds. Confirm completion with the repository's available checks.

Written by the indexing model from the issue text.