refactor(notifications): fetch from backend API instead of local generation

Rewrite store/notifications.ts to fetch via listNotifications
API and remove local generateId-based notification creation.
The store now acts as a simple cache with fetch/invalidate methods.
Header unread count reads from this API-backed cache.

app/(account)/notifications/page.tsx

@@ -10,6 +10,7 @@ import { toApiError } from "@/lib/errors"
 import { notifyInfo } from "@/lib/toast"
 import type { Notification } from "@/lib/types"
 import { cn } from "@/lib/utils"
+import { useNotificationStore } from "@/store/notifications"
 import { Bell, CheckCheck, Loader2, MessageSquare, ShoppingBag } from "lucide-react"
 import Link from "next/link"
 import { useCallback, useEffect, useMemo, useRef, useState } from "react"
@@ -100,31 +101,37 @@ export default function NotificationsPage() {
   const [loading, setLoading] = useState(true)
   const [loadingError, setLoadingError] = useState<string | null>(null)
   const [markingAll, setMarkingAll] = useState(false)
+  const setStoreNotifications = useNotificationStore((state) => state.setNotifications)
+  const markStoreAllRead = useNotificationStore((state) => state.markAllRead)
 
-  const loadNotifications = useCallback(async function loadNotifications() {
-    setLoading(true)
-    setLoadingError(null)
+  const loadNotifications = useCallback(
+    async function loadNotifications() {
+      setLoading(true)
+      setLoadingError(null)
 
-    try {
-      const res = await requestWithAuth(() => listNotifications({ offset: 0, limit: 50 }), {
-        onUnauthorized: () => loadNotifications(),
-      })
+      try {
+        const res = await requestWithAuth(() => listNotifications({ offset: 0, limit: 50 }), {
+          onUnauthorized: () => loadNotifications(),
+        })
 
-      if (!mountedRef.current) return
+        if (!mountedRef.current) return
 
-      if (res === null) {
+        if (res === null) {
+          setLoading(false)
+          return
+        }
+
+        setNotifications(res)
+        setStoreNotifications(res)
         setLoading(false)
-        return
+      } catch (err: unknown) {
+        if (!mountedRef.current) return
+        setLoading(false)
+        setLoadingError(toApiError(err).msg)
       }
-
-      setNotifications(res)
-      setLoading(false)
-    } catch (err: unknown) {
-      if (!mountedRef.current) return
-      setLoading(false)
-      setLoadingError(toApiError(err).msg)
-    }
-  }, [])
+    },
+    [setStoreNotifications],
+  )
 
   useEffect(() => {
     mountedRef.current = true
@@ -134,32 +141,36 @@ export default function NotificationsPage() {
     }
   }, [loadNotifications])
 
-  const markAllAsRead = useCallback(async function markAllAsRead() {
-    if (markAllPendingRef.current) return
+  const markAllAsRead = useCallback(
+    async function markAllAsRead() {
+      if (markAllPendingRef.current) return
 
-    markAllPendingRef.current = true
-    setMarkingAll(true)
+      markAllPendingRef.current = true
+      setMarkingAll(true)
 
-    try {
-      const res = await requestWithAuth(() => markAllNotificationsAsRead(), {
-        onUnauthorized: () => markAllAsRead(),
-      })
+      try {
+        const res = await requestWithAuth(() => markAllNotificationsAsRead(), {
+          onUnauthorized: () => markAllAsRead(),
+        })
 
-      if (!mountedRef.current) return
+        if (!mountedRef.current) return
 
-      if (res === null) {
-        return
+        if (res === null) {
+          return
+        }
+
+        setNotifications((prev) => prev.map((n) => (n.read ? n : { ...n, read: true })))
+        markStoreAllRead()
+      } catch (err: unknown) {
+        if (!mountedRef.current) return
+        notifyInfo(toApiError(err).msg)
+      } finally {
+        markAllPendingRef.current = false
+        if (mountedRef.current) setMarkingAll(false)
       }
-
-      setNotifications((prev) => prev.map((n) => (n.read ? n : { ...n, read: true })))
-    } catch (err: unknown) {
-      if (!mountedRef.current) return
-      notifyInfo(toApiError(err).msg)
-    } finally {
-      markAllPendingRef.current = false
-      if (mountedRef.current) setMarkingAll(false)
-    }
-  }, [])
+    },
+    [markStoreAllRead],
+  )
 
   const unreadCount = useMemo(
     () => notifications.filter((notification) => !notification.read).length,