Export: fix VideoEncoder.configure TypeError on Chrome

probeExportCodec returned codec/muxerCodec but not config, so the
pre-probed pick used by the software-encoding warning path passed
undefined to VideoEncoder.configure, which Chrome rejects as "not of
type VideoEncoderConfig". Include config in the probe result and thread
it through exportSegment (test render was still reprobing and ignoring
the pick).

Also prefer the browser-negotiated config from isConfigSupported when
available — it is guaranteed valid for configure (covers new required
fields), whereas our minimal config had started failing validation on
Chrome despite isConfigSupported reporting "supported".

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

flow-state/src/main.js

@@ -658,7 +658,7 @@ async function runExport(segment) {
         const exporter = new Exporter(state.show);
         const blob = segment
             ? await exportSegment(state.show, state.show.timeline.frame,
-                { seconds: 20, preset, onProgress: exportProgress, exporter })
+                { seconds: 20, preset, onProgress: exportProgress, exporter, videoPick: pick })
             : await exporter.export({ preset, onProgress: exportProgress, videoPick: pick });
 
         const suffix = segment ? `-segment-${state.show.timeline.frame}` : '';