Add --force option to sol import and fix SystemExit message display
- Fix sol.py run_command() to print SystemExit string messages to stderr
(previously string messages were silently swallowed)
- Add --force flag to importer that deletes existing import directory
and starts fresh, with clear error message guiding users to use it
- Move shutil import to top of file per project conventions
- Add test for string SystemExit handling
Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>