The show command was crashing with a nil pointer dereference when
accessing issue.CompactionLevel. This occurred due to two issues in
the daemon mode response handling:
1. The IssueDetails struct incorrectly embedded *types.Issue as a
pointer, causing the JSON unmarshaling to leave it nil. Changed
to embed types.Issue directly.
2. Missing null check for non-existent issues. The daemon returns
null when an issue is not found, which wasn't handled properly.
Added explicit null checking before parsing the response to provide
a clear error message when issues don't exist.
Fixes panic when running: bd show <non-existent-id>
86988fccf4