Refactor list_sessions to reuse the summary dict already computed by
_session_list_dict instead of recalculating total_msgs, sorted_sessions,
most_recent, and oldest independently.
The rich table summary panel now reads directly from data["summary"],
ensuring JSON and rich table output are always consistent and the
summary logic lives in exactly one place (_session_list_dict).
Add Behave feature (session_list_summary_dedup.feature) with 6 scenarios
verifying that JSON and rich table summary values are consistent across
all required fields: total, most_recent, oldest, total_messages, storage.
ISSUES CLOSED: #3046
freemo