Improve session display by showing parallel events in a responsive grid

Adjust SessionTimeline component to render parallel sessions in a responsive grid layout (1 column on mobile, 2 on tablet, 3 on desktop) instead of a vertical list.

Replit-Commit-Author: Agent
Replit-Commit-Session-Id: 72d1ee0d-43f0-4151-941b-cf0c139bc10a
Replit-Commit-Checkpoint-Type: intermediate_checkpoint
Replit-Commit-Event-Id: 6abb2203-b951-4077-9e84-dfdc8c893f93
Replit-Commit-Screenshot-Url: https://storage.googleapis.com/screenshot-production-us-central1/04133160-d2cd-42c9-82f0-4e08d800b951/72d1ee0d-43f0-4151-941b-cf0c139bc10a/wfEqveN
Replit-Helium-Checkpoint-Created: true

Author: marcselman

client/src/components/SessionTimeline.tsx

@@ -78,7 +78,7 @@ export function SessionTimeline({
               <div className="mt-2 h-3 w-3 rounded-full bg-primary" />
             </div>
 
-            <div className="flex-1 space-y-3 pt-1">
+            <div className="flex-1 pt-1 grid grid-cols-1 md:grid-cols-2 xl:grid-cols-3 gap-3">
               {slotSessions.map((session) => {
                 const isRegistered = userEmail
                   ? isEmailInList(userEmail, session.attendees)