feat: show all sessions in hexbin visualization without limits

- Remove 200-session limit to display complete conversation history
- Show full temporal range across entire session dataset
- Enable comprehensive activity pattern analysis
- Maintain performance through hexbin aggregation
- Reveal long-term trends and usage evolution
- Display true session density without artificial constraints

ui/desktop/src/components/sessions/SessionTimelineView.tsx

@@ -40,8 +40,8 @@ const SessionTimelineView: React.FC<SessionTimelineViewProps> = ({
 
     // Sort sessions by creation date (newest first)
     const sortedSessions = [...sessions]
-      .sort((a, b) => new Date(b.created_at).getTime() - new Date(a.created_at).getTime())
-      .slice(0, 200); // Limit for performance
+      .sort((a, b) => new Date(b.created_at).getTime() - new Date(a.created_at).getTime());
+    // Show ALL sessions - no limit
 
     // Convert sessions to points for hexbin
     const points: HexbinPoint[] = sortedSessions.map((session, index) => {