fix: waveform not rendering on voice messages after thread switch

The call wave sync watcher fired before DOM was updated (flush: 'pre'),
so ref callbacks hadn't registered host elements yet. Changed to
flush: 'post' so WaveSurfer instances are created after DOM refs exist.
Also fixed getCallItem to read from clientTimelineItems (source of truth)
instead of visibleThreadItems which could be stale.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

frontend/app/components/workspace/CrmWorkspaceApp.vue

@@ -588,7 +588,7 @@ const threadStreamItems = computed(() => {
   return rows.sort((a, b) => a.at.localeCompare(b.at));
 });
 
-// Sync call waves when thread stream changes
+// Sync call waves when thread stream changes (flush: 'post' ensures DOM refs are registered)
 watch(
   () => threadStreamItems.value.map((entry: any) => `${entry.kind}:${entry.id}`).join("|"),
   () => {
@@ -597,10 +597,15 @@ watch(
         .filter((entry: any) => entry.kind === "call")
         .map((entry: any) => entry.item.id as string),
     );
-    const getCallItem = (id: string) =>
-      visibleThreadItems.value.find((item) => item.id === id && item.kind === "call");
+    const getCallItem = (id: string) => {
+      const timelineItem = clientTimelineItems.value.find(
+        (entry) => entry.contentType === "message" && entry.message?.id === id && entry.message?.kind === "call",
+      );
+      return timelineItem?.message ?? undefined;
+    };
     void _syncCommCallWavesRaw(activeCallIds, getCallItem);
   },
+  { flush: "post" },
 );
 
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