feat: Add floating "See Friends" button when list is closed

Shows a prominent button at bottom-left (mobile) or top-left (desktop)
to reopen the friends list after closing it.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

src/app/[slug]/page.tsx

@@ -383,6 +383,18 @@ export default function RoomPage() {
           </div>
         )}
 
+        {/* Floating "See Friends" button when participant list is hidden */}
+        {!showParticipants && (
+          <button
+            onClick={() => setShowParticipants(true)}
+            className="absolute bottom-6 left-4 md:top-4 md:bottom-auto flex items-center gap-2 px-4 py-2.5 rounded-full bg-rmaps-dark/90 backdrop-blur border border-white/20 hover:bg-rmaps-dark hover:border-white/30 transition-colors shadow-lg z-20"
+          >
+            <span className="text-lg">👥</span>
+            <span className="text-sm font-medium">See Friends</span>
+            <span className="text-xs text-white/60">({participants.length})</span>
+          </button>
+        )}
+
         {/* Connection status indicator */}
         {!isConnected && (
           <div className="absolute top-4 left-1/2 -translate-x-1/2 bg-yellow-500/90 text-black text-sm px-3 py-1.5 rounded-full z-30">