fix: screenshare rendering, voice panel layout, SW cache bust with git SHA

- VideoGrid: add screen share track display with proper sizing
- participantToVoice: detect ScreenShare + ScreenShareAudio tracks
- VoicePanel: flex layout, no scroll, tiles dynamically fill space
- VoiceChannel: show screen/camera icons in participant list
- vite.config: inject git SHA into SW CACHE_VERSION on build

web/src/components/Layout.tsx

@@ -219,7 +219,7 @@ export function Layout() {
                 <Outlet />
               </div>
               {currentVoiceRoom && (
-                <div className={`flex-1 min-h-0 flex-col overflow-y-auto bg-gb-bg ${activeTab === 'voice' ? 'flex' : 'hidden'}`}>
+                <div className={`flex-1 min-h-0 flex-col ${activeTab === 'voice' ? 'flex' : 'hidden'}`}>
                   <VoicePanel />
                 </div>
               )}