refactor: 优化参与者列表生成逻辑

- 在 `MeetingPreviewView.tsx` 中更新 `participants` 的生成逻辑，当 `meeting?.participants` 为空时，从 `transcripts` 中提取唯一发言人并生成列表

imeeting-h5/src/components/preview/MeetingPreviewView.tsx

@@ -180,7 +180,19 @@ export default function MeetingPreviewView({
     () => buildMeetingAnalysis(meeting?.analysis, meeting?.summaryContent, meeting?.tags || ""),
     [meeting?.analysis, meeting?.summaryContent, meeting?.tags],
   );
-  const participants = useMemo(() => splitDisplayItems(meeting?.participants), [meeting?.participants]);
+  const participants = useMemo(() => {
+    const list = splitDisplayItems(meeting?.participants);
+    if (list.length > 0) return list;
+
+    const uniqueSpeakers = new Set<string>();
+    for (const item of transcripts) {
+      const speakerKey = item.speakerName || item.speakerLabel || item.speakerId;
+      if (speakerKey) {
+        uniqueSpeakers.add(speakerKey);
+      }
+    }
+    return Array.from(uniqueSpeakers);
+  }, [meeting?.participants, transcripts]);
   const tags = useMemo(() => splitDisplayItems(meeting?.tags), [meeting?.tags]);
   const playbackAudioUrl = useMemo(() => resolveMeetingPlaybackAudioUrl(meeting), [meeting]);
   const statusMeta = STATUS_META[meeting?.status || 0] || {