修复：补齐多项目公屏叫号播报

需求：管理员公屏在员工叫号后需播放项目名与号码。
实现：复用单项目号码播报格式，按项目跟踪新批次并播报项目名加号码，补充回归测试。

web/src/pages/PublicDisplayCenterPage.tsx

@@ -1,13 +1,48 @@
+import { useEffect, useRef } from "react";
 import { api } from "../api";
 import { FeedbackBanner, FreshnessBanner, LoadingState } from "../components/Feedback";
 import { usePollingResource } from "../hooks/usePollingResource";
-import { isTimestampStale } from "../lib/format";
+import { formatCallAnnouncement, isTimestampStale } from "../lib/format";
+import type { CallBatchDto } from "../types";
 import { DisplayCenter } from "./AdminPage";
 
+function projectCurrentBatch(value: unknown): CallBatchDto | null {
+  return value && typeof value === "object" ? value as CallBatchDto : null;
+}
+
 export function PublicDisplayCenterPage() {
   const resource = usePollingResource((signal) => api.displayOverview(signal), { intervalMs: 5_000 });
   const data = resource.data;
   const stale = Boolean(data) && isTimestampStale(resource.lastClientSuccessAt, 30_000);
+  const lastCallsRef = useRef<Map<string, string | null> | null>(null);
+  useEffect(() => {
+    if (!data) return;
+    const previousCalls = lastCallsRef.current;
+    const nextCalls = new Map<string, string | null>();
+    const announcements: string[] = [];
+    for (const project of data.projects) {
+      const batch = projectCurrentBatch(project.current_batch);
+      const key = batch ? `${batch.batch_number}:${batch.called_at ?? ""}` : null;
+      nextCalls.set(project.id, key);
+      if (!previousCalls?.has(project.id) || !key || previousCalls.get(project.id) === key) continue;
+      const announcement = formatCallAnnouncement(batch);
+      if (announcement) announcements.push(`${project.name}，${announcement}`);
+    }
+    lastCallsRef.current = nextCalls;
+    if (
+      !announcements.length
+      || !("speechSynthesis" in window)
+      || typeof SpeechSynthesisUtterance === "undefined"
+    ) return;
+
+    window.speechSynthesis.cancel();
+    for (const announcement of announcements) {
+      const utterance = new SpeechSynthesisUtterance(announcement);
+      utterance.lang = "zh-CN";
+      utterance.rate = 0.9;
+      window.speechSynthesis.speak(utterance);
+    }
+  }, [data]);
 
   return (
     <div className="app-shell app-shell--admin app-shell--no-primary-action">