feat(notify): convert email lists to NotifyEmailEntry struct with toggle support

- Change balance_notify_extra_emails and account_quota_notify_emails
  from []string to []NotifyEmailEntry{email, disabled, verified}
- Add per-email enable/disable toggle for both user and admin notifications
- Add PUT /user/notify-email/toggle API endpoint
- Fix critical bug: API key auth cache snapshot missing balance notify
  fields (Email, Username, BalanceNotifyEnabled, etc.), causing
  notifications to never fire on cached request paths
- Bump cache snapshot version 3→4 to invalidate stale entries
- Add SQL migration 104 to convert old format data
- Backward compatible: parseNotifyEmails auto-detects old/new format
- User balance notify: max 3 emails (primary + 2 extra)
- Admin quota notify: unlimited emails, each with toggle

frontend/src/api/user.ts

@@ -4,7 +4,7 @@
  */
 
 import { apiClient } from './client'
-import type { User, ChangePasswordRequest } from '@/types'
+import type { User, ChangePasswordRequest, NotifyEmailEntry } from '@/types'
 
 /**
  * Get current user profile
@@ -24,7 +24,7 @@ export async function updateProfile(profile: {
   username?: string
   balance_notify_enabled?: boolean
   balance_notify_threshold?: number | null
-  balance_notify_extra_emails?: string[]
+  balance_notify_extra_emails?: NotifyEmailEntry[]
 }): Promise<User> {
   const { data } = await apiClient.put<User>('/user', profile)
   return data
@@ -73,13 +73,24 @@ export async function removeNotifyEmail(email: string): Promise<void> {
   await apiClient.delete('/user/notify-email', { data: { email } })
 }
 
+/**
+ * Toggle a notify email's disabled state
+ * @param email - Email address (empty string for primary email placeholder)
+ * @param disabled - Whether to disable the email
+ */
+export async function toggleNotifyEmail(email: string, disabled: boolean): Promise<User> {
+  const { data } = await apiClient.put<User>('/user/notify-email/toggle', { email, disabled })
+  return data
+}
+
 export const userAPI = {
   getProfile,
   updateProfile,
   changePassword,
   sendNotifyEmailCode,
   verifyNotifyEmail,
-  removeNotifyEmail
+  removeNotifyEmail,
+  toggleNotifyEmail
 }
 
 export default userAPI