✨ FEATURE: Add PayloadCMS task for queuing template emails

- Add sendTemplateEmailTask with comprehensive input schema
- Support template rendering, email parsing, and scheduling
- Include TypeScript interface SendTemplateEmailInput for type safety
- Add task to exports for easy import and usage
- Support custom email collection fields via extensible input
- Add comprehensive documentation with usage examples

Users can now:
✅ Import and add task to their Payload jobs configuration
✅ Queue emails programmatically via payload.jobs.queue()
✅ Use admin panel form interface for manual email queuing
✅ Get full TypeScript support with proper input types
✅ Extend with custom fields from their email collection

Example usage:
```typescript
import { sendTemplateEmailTask } from '@xtr-dev/payload-mailing'

// Add to Payload config
export default buildConfig({
  jobs: { tasks: [sendTemplateEmailTask] }
})

// Queue from code
await payload.jobs.queue({
  task: 'send-template-email',
  input: {
    templateSlug: 'welcome',
    to: ['user@example.com'],
    variables: { name: 'John' }
  }
})
```

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

src/index.ts

@@ -11,6 +11,10 @@ export { MailingService } from './services/MailingService.js'
 export { default as EmailTemplates, createEmailTemplatesCollection } from './collections/EmailTemplates.js'
 export { default as Emails } from './collections/Emails.js'
 
+// Tasks
+export { sendTemplateEmailTask, default as sendTemplateEmailTaskDefault } from './tasks/sendTemplateEmailTask.js'
+export type { SendTemplateEmailInput } from './tasks/sendTemplateEmailTask.js'
+
 // Jobs are integrated into the plugin configuration
 
 // Utility functions for developers