✨(frontend) add keepAlive option to Panel component

Implement new keepAlive property for Panel component to control DOM retention
when panel is closed. When false, panel content is unmounted from DOM on
close, resetting scroll position and input states. Provides finer control
over panel behavior and memory management.

src/frontend/src/features/rooms/livekit/components/SidePanel.tsx

@@ -110,9 +110,10 @@ const StyledSidePanel = ({
 type PanelProps = {
   isOpen: boolean
   children: React.ReactNode
+  keepAlive?: boolean
 }
 
-const Panel = ({ isOpen, children }: PanelProps) => (
+const Panel = ({ isOpen, keepAlive = true, children }: PanelProps) => (
   <div
     style={{
       display: isOpen ? 'inherit' : 'none',
@@ -121,7 +122,7 @@ const Panel = ({ isOpen, children }: PanelProps) => (
       flexGrow: 1,
     }}
   >
-    {children}
+    {keepAlive || isOpen ? children : null}
   </div>
 )