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/VoiceChannel.tsx

@@ -90,6 +90,8 @@ export function VoiceChannel({ channelId, channelName }: VoiceChannelProps) {
                 <span className={p.isSpeaking ? 'text-gb-green' : ''}>
                   {p.username}
                 </span>
+                {p.isScreenSharing && <span className="text-gb-aqua" title="Sharing screen">🖥</span>}
+                {p.hasVideo && <span className="text-gb-orange" title="Camera on">🎥</span>}
                 
                 {!isMe && (
                   <div className="ml-auto opacity-0 group-hover:opacity-100 flex items-center gap-1">