feat: add payment management improvements and reminder emails

- Add option to approve/reject payments without sending notification emails
  (checkbox in review popup, default enabled)
- Add payment reminder email template and send functionality
- Track when reminder emails are sent (reminderSentAt field)
- Display reminder sent timestamp in payment review popup
- Make payment review popup scrollable for better UX
- Add payment-reminder template to email system (available in admin emails)

backend/src/db/schema.ts

@@ -115,6 +115,7 @@ export const sqlitePayments = sqliteTable('payments', {
   paidAt: text('paid_at'),
   paidByAdminId: text('paid_by_admin_id'),
   adminNote: text('admin_note'), // Internal admin notes
+  reminderSentAt: text('reminder_sent_at'), // When payment reminder email was sent
   createdAt: text('created_at').notNull(),
   updatedAt: text('updated_at').notNull(),
 });
@@ -405,6 +406,7 @@ export const pgPayments = pgTable('payments', {
   paidAt: timestamp('paid_at'),
   paidByAdminId: uuid('paid_by_admin_id'),
   adminNote: pgText('admin_note'),
+  reminderSentAt: timestamp('reminder_sent_at'), // When payment reminder email was sent
   createdAt: timestamp('created_at').notNull(),
   updatedAt: timestamp('updated_at').notNull(),
 });