offline cache

**Is your feature request related to a problem? Please describe.**
it's not possible to develop offline - or with a slow connection - easily, eg when traveling in trains or planes.

**Describe the solution you'd like**
the cli should cache proxied content by default (with a reasonable limit) and detect offline conditions.
once detected, it should either transparently switch to the cached content, or offer to user to do so.

all this should also be configurable via cmd line arguments.

Start by locating the CLI entry point, proxied-content handling, and command-line argument definitions. Check how the CLI currently behaves without a network connection and whether any cache-related configuration exists. Done means bounded caching works by default, offline conditions are detected, cached content can be used or selected, and all behavior is configurable through command-line arguments.

Written by the indexing model from the issue text.