feat(smtp): implement built-in SMTP server for mail ingestion

- Add lightweight SMTP server support using `lettre` and `tokio`.
- Implement `DATA_SMTP_INGEST` permission check for inbound mail.
- Support real-time email archiving via SMTP protocol.
- Integrate with existing EML index manager for automated indexing.

web/src/api/users/api.ts

@@ -40,6 +40,7 @@ export function getPermissions(t: (key: string) => string) {
         { label: t('permission.data.delete'), value: 'data:delete' },
         { label: t('permission.data.export_batch'), value: 'data:export:batch' },
         { label: t('permission.data.import_batch'), value: 'data:import:batch' },
+        { label: t('permission.data.smtp_ingest'), value: 'data:smtp:ingest' },
     ]
 }