zebra-spaces: log every screen/camera/game ontrack with state — diagnostic

Listener reports seeing host's screen-share but NOT camera-share on
rejoin. SFU log shows both pubs alive + addPubToSub fires for the
new sub, but the listener-side visible result diverges between
screen and camera. Add a log line that captures everything we know
when each video-kind track lands:

  sfu ontrack: kind=camera pub=abc12345
                track=video mute=true state=live

Fields:
- kind: which routing branch we took
- pub: short pubHex prefix
- track.kind: should be 'video' for screen/camera/game
- track.muted: initial mute state (true is normal pre-RTP)
- track.readyState: 'live' = good, anything else = bad

Fox can paste the lines so we can see whether (a) the camera
ontrack never fires (SFU subscribe SDP is dropping it), (b) it
fires with track.muted=true and stays that way (no RTP arriving),
or (c) it fires healthy and gets pruned by some downstream bug.

web/zebra-spaces.html

@@ -2150,6 +2150,10 @@ async function sfuSubscribe(){
         }
       } catch(_){}
     }
+    if (kind === 'screen' || kind === 'camera' || kind === 'game'){
+      logLine('', 'sfu ontrack: kind=' + kind + ' pub=' + shortHex(pubHex) +
+                  ' track=' + ev.track.kind + ' mute=' + ev.track.muted + ' state=' + ev.track.readyState);
+    }
     if (kind === 'screen'){
       screenStreams.set(pubHex, ev.streams[0]);
       renderScreenTile(pubHex, ev.streams[0]);
@@ -3505,8 +3509,8 @@ logLine('', 'ready — pick a handle, type a rendezvous code, enter the space');
 
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