* feat: add proration invoice and reminder email templates
Add email templates for monthly proration billing notifications:
- ProrationInvoiceEmail: Sent when invoice is created for additional seats
- ProrationReminderEmail: Sent 7 days later if invoice remains unpaid
Includes:
- React email templates using V2BaseEmailHtml
- BaseEmail classes for rendering
- Billing email service functions
- Translation keys for email content
Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
* fix: use allSettled
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Co-authored-by: Claude Opus 4.5 <noreply@anthropic.com>
