Task #393: Coalesce notification sound bursts on app open

User reported a flood of chimes when opening Tx OS while several
notifications were pending. Two complementary fixes:

1. Player throttle bumped from 600 ms → 3000 ms in
   artifacts/tx-os/src/lib/notification-sounds.ts. Bursts of real-time
   events now produce a single chime instead of several overlapping ones.

2. Socket warmup gate added in
   artifacts/tx-os/src/hooks/use-notifications-socket.ts:
   - Track connectedAtRef (useRef<number>), set on effect mount and on
     each socket "connect" event using performance.now().
   - In the notification_created handler, after mute / per-channel
     gates but before notificationPlayer.play(...), suppress
     audio + vibration when within the 3 s warmup window.
   - UI/badge invalidation still runs — only sound is silenced during
     the warmup, so the user sees notifications appear without an
     alarm-like welcome.

All existing gates preserved (global mute, per-channel sound/vibration,
autoplay-blocked toast hint, per-meeting playedRef dedupe).

No deviations. tx-os typecheck passes.

artifacts/tx-os/src/hooks/use-notifications-socket.ts

@@ -1,4 +1,4 @@
-import { useEffect } from "react";
+import { useEffect, useRef } from "react";
 import { io } from "socket.io-client";
 import { useQueryClient } from "@tanstack/react-query";
 import {
@@ -19,17 +19,31 @@ import { notificationPlayer } from "@/lib/notification-sounds";
 
 const BASE = import.meta.env.BASE_URL.replace(/\/$/, "");
 
+const SOCKET_WARMUP_MS = 3000;
+const nowMs = () =>
+  typeof performance !== "undefined" ? performance.now() : Date.now();
+
 export function useNotificationsSocket() {
   const { user } = useAuth();
   const queryClient = useQueryClient();
+  const connectedAtRef = useRef<number>(0);
 
   useEffect(() => {
     if (!user) return;
 
+    // Suppress chimes for the first few seconds after the socket
+    // connects so any pending notifications that flush in on page
+    // load don't all play sounds back-to-back.
+    connectedAtRef.current = nowMs();
+
     const socket = io(window.location.origin, {
       path: `${BASE}/api/socket.io`,
     });
 
+    socket.on("connect", () => {
+      connectedAtRef.current = nowMs();
+    });
+
     socket.on("notification_created", (payload?: { type?: string }) => {
       queryClient.invalidateQueries({ queryKey: getListNotificationsQueryKey() });
       queryClient.invalidateQueries({ queryKey: getGetHomeStatsQueryKey() });
@@ -52,6 +66,10 @@ export function useNotificationsSocket() {
       if (isOrder && !user.notifyOrdersEnabled) return;
       if (isMeeting && !user.notifyMeetingsEnabled) return;
       if (!isOrder && !isMeeting) return;
+      // Skip audio/vibration during the warmup window — UI/badge
+      // counts (above) still update, but we stay silent so a
+      // page-load flush doesn't sound like an alarm.
+      if (nowMs() - connectedAtRef.current < SOCKET_WARMUP_MS) return;
       const soundId = isOrder
         ? user.notificationSoundOrder
         : user.notificationSoundMeeting;