feat: add per-account daily rate limit for outbound emails (#13411)
Introduce a daily cap on non-channel outbound emails to prevent abuse.
Fixes https://linear.app/chatwoot/issue/CW-6418/ses-incident-jan-28
## Type of change
- [x] New feature (non-breaking change which adds functionality)
- [x] Breaking change (fix or feature that would cause existing
functionality not to work as expected)
## Summary
- Adds a Redis-based daily counter to rate limit outbound emails per
account, preventing email abuse
- Covers continuity emails (WebWidget/API), conversation transcripts,
and agent notifications
- Email channel replies are excluded (paid feature, not abusable)
- Adds account suspension check in `ConversationReplyMailer` to block
already-queued emails for suspended accounts
## Limit Resolution Hierarchy
1. Per-account override (`account.limits['emails']`) — SuperAdmin
configurable
2. Enterprise plan-based (`ACCOUNT_EMAILS_PLAN_LIMITS`
InstallationConfig)
3. Global default (`ACCOUNT_EMAILS_LIMIT` InstallationConfig, default:
100)
4. Fallback (`ChatwootApp.max_limit` — effectively unlimited)
## Enforcement Points
| Path | Where | Behavior |
|------|-------|----------|
| WebWidget/API continuity |
`SendEmailNotificationService#should_send_email_notification?` |
Silently skipped |
| Widget transcript | `Widget::ConversationsController#transcript` |
Returns 429 |
| API transcript | `ConversationsController#transcript` | Returns 429 |
| Agent notifications | `Notification::EmailNotificationService#perform`
| Silently skipped |
| Email channel replies | Not rate limited | Paid feature |
| Suspended accounts | `ConversationReplyMailer` | Blocked at mailer
level |
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