fix(session): add name field and summary section to session list JSON output

- Add name field to each session entry in JSON output
- Add summary section with total, most_recent, oldest, total_messages, storage fields
- Move total from top-level into summary section
- Most recent/oldest show session name if available, otherwise truncated ID
- Storage field is placeholder (0 KB) pending actual storage calculation implementation

Fixes #1508

src/cleveragents/cli/commands/session.py

@@ -123,20 +123,42 @@ def _session_summary_dict(session: Session) -> OrderedDict[str, Any]:
 
 
 def _session_list_dict(sessions: list[Session]) -> dict[str, Any]:
-    """Build the list output with summary stats."""
+    """Build the list output with summary stats per spec."""
     items = []
     for s in sessions:
         items.append(
             {
                 "id": s.session_id,
+                "name": s.name or None,
                 "actor": s.actor_name or "(none)",
                 "messages": s.message_count,
                 "updated": s.updated_at.isoformat(),
             }
         )
+
+    # Build summary section per spec
+    total_messages = sum(s.message_count for s in sessions)
+
+    # Find most recent and oldest sessions
+    if sessions:
+        sorted_sessions = sorted(sessions, key=lambda x: x.updated_at, reverse=True)
+        most_recent = sorted_sessions[0].name or sorted_sessions[0].session_id[:8]
+        oldest = sorted_sessions[-1].name or sorted_sessions[-1].session_id[:8]
+    else:
+        most_recent = None
+        oldest = None
+
+    summary = {
+        "total": len(sessions),
+        "most_recent": most_recent,
+        "oldest": oldest,
+        "total_messages": total_messages,
+        "storage": "0 KB",  # Placeholder - actual storage calculation not implemented
+    }
+
     return {
         "sessions": items,
-        "total": len(sessions),
+        "summary": summary,
     }