Add comprehensive test suite mapping to PR #184 test plan:
- Create multiple variants with unique ports (8318-8417)
- Verify port persistence in config and separate config-{port}.yaml
- Run multiple variants concurrently with isolated sessions
- Verify list shows port column for each variant
- Remove variant cleans config, session, and port-specific files
25 new tests covering edge cases:
- Port exhaustion (100 variant max)
- Port reuse after deletion
- Legacy variants without port field
- Stale session cleanup for dead PIDs
- Default port special handling (sessions.json)
