refactor(frontend): simplify event chat UI

- Replace "Edit heats" button with icon-only version
- Remove connection status indicator (show "Disconnected" warning only when offline)
- Remove event location from header
- Hide Participants tab on desktop (sidebar already visible)
- Remove "Participants" header from sidebar on desktop

frontend/src/pages/EventChatPage.jsx

@@ -359,12 +359,7 @@ const EventChatPage = () => {
             <div className="flex items-start justify-between">
               <div className="flex-1">
                 <h2 className="text-2xl font-bold">{event.name}</h2>
-                <p className="text-primary-100 text-sm">{event.location}</p>
                 <div className="mt-2 flex items-center gap-3">
-                  <span className={`text-xs px-2 py-1 rounded ${isConnected ? 'bg-green-500' : 'bg-red-500'}`}>
-                    {isConnected ? '● Connected' : '● Disconnected'}
-                  </span>
-
                   {/* My Heats Display */}
                   {myHeats.length > 0 && (
                     <div className="flex items-center gap-2">
@@ -382,15 +377,15 @@ const EventChatPage = () => {
                 {myHeats.length > 0 && (
                   <button
                     onClick={() => setShowHeatsModal(true)}
-                    className="flex items-center gap-2 px-3 py-2 bg-primary-700 hover:bg-primary-800 rounded-md transition-colors text-sm"
+                    className="p-2 bg-primary-700 hover:bg-primary-800 rounded-md transition-colors"
+                    title="Edit heats"
                   >
                     <Edit2 className="w-4 h-4" />
-                    Edit Heats
                   </button>
                 )}
                 <button
                   onClick={() => setShowLeaveModal(true)}
-                  className="flex items-center gap-2 px-3 py-2 bg-red-600 hover:bg-red-700 rounded-md transition-colors text-sm"
+                  className="p-2 bg-red-600 hover:bg-red-700 rounded-md transition-colors"
                   title="Leave Event"
                 >
                   <LogOut size={16} />
@@ -399,6 +394,14 @@ const EventChatPage = () => {
             </div>
           </div>
 
+          {/* Disconnected Warning - show only when disconnected */}
+          {!isConnected && (
+            <div className="bg-red-600 text-white px-4 py-2 text-sm flex items-center gap-2">
+              <AlertTriangle className="w-4 h-4" />
+              <span>Disconnected</span>
+            </div>
+          )}
+
           {/* Heats Banner */}
           {showHeatsBanner && (
             <HeatsBanner
@@ -425,7 +428,7 @@ const EventChatPage = () => {
               </button>
               <button
                 onClick={() => setActiveTab('participants')}
-                className={`flex items-center gap-2 px-4 py-3 text-sm font-medium border-b-2 transition-colors ${
+                className={`lg:hidden flex items-center gap-2 px-4 py-3 text-sm font-medium border-b-2 transition-colors ${
                   activeTab === 'participants'
                     ? 'border-primary-600 text-primary-600 bg-white'
                     : 'border-transparent text-gray-500 hover:text-gray-700 hover:border-gray-300'
@@ -467,6 +470,7 @@ const EventChatPage = () => {
                     hideMyHeats={hideMyHeats}
                     onHideMyHeatsChange={setHideMyHeats}
                     onMatchWith={handleMatchWith}
+                    showHeader={false}
                   />
                 </div>