feat(notify): improve balance notify card UX

- Show system default threshold as placeholder in custom threshold input
- Display user's primary email with "Primary" badge
- Support adding multiple pending emails before verification
- Each pending email has independent send/verify/resend flow
- Expose balance_low_notify_threshold in PublicSettings API
- Clean up timers on unmount to prevent leaks

frontend/src/views/user/ProfileView.vue

@@ -19,6 +19,8 @@
         :enabled="user.balance_notify_enabled ?? true"
         :threshold="user.balance_notify_threshold"
         :extra-emails="user.balance_notify_extra_emails ?? []"
+        :system-default-threshold="systemDefaultThreshold"
+        :user-email="user.email"
       />
       <ProfilePasswordForm />
       <ProfileTotpCard />
@@ -41,11 +43,12 @@ import { Icon } from '@/components/icons'
 const { t } = useI18n(); const authStore = useAuthStore(); const user = computed(() => authStore.user)
 const contactInfo = ref('')
 const balanceLowNotifyEnabled = ref(false)
+const systemDefaultThreshold = ref(0)
 
 const WalletIcon = { render: () => h('svg', { fill: 'none', viewBox: '0 0 24 24', stroke: 'currentColor', 'stroke-width': '1.5' }, [h('path', { d: 'M21 12a2.25 2.25 0 00-2.25-2.25H15a3 3 0 11-6 0H5.25A2.25 2.25 0 003 12' })]) }
 const BoltIcon = { render: () => h('svg', { fill: 'none', viewBox: '0 0 24 24', stroke: 'currentColor', 'stroke-width': '1.5' }, [h('path', { d: 'm3.75 13.5 10.5-11.25L12 10.5h8.25L9.75 21.75 12 13.5H3.75z' })]) }
 const CalendarIcon = { render: () => h('svg', { fill: 'none', viewBox: '0 0 24 24', stroke: 'currentColor', 'stroke-width': '1.5' }, [h('path', { d: 'M6.75 3v2.25M17.25 3v2.25' })]) }
 
-onMounted(async () => { try { const s = await authAPI.getPublicSettings(); contactInfo.value = s.contact_info || ''; balanceLowNotifyEnabled.value = s.balance_low_notify_enabled ?? false } catch (error) { console.error('Failed to load contact info:', error) } })
+onMounted(async () => { try { const s = await authAPI.getPublicSettings(); contactInfo.value = s.contact_info || ''; balanceLowNotifyEnabled.value = s.balance_low_notify_enabled ?? false; systemDefaultThreshold.value = s.balance_low_notify_threshold ?? 0 } catch (error) { console.error('Failed to load settings:', error) } })
 const formatCurrency = (v: number) => `$${v.toFixed(2)}`
 </script>