Add sendEmail workflow with immediate processing option

- Create sendEmailWorkflow as a Payload workflow alternative to task
- Add processImmediately option (disabled by default) to send emails immediately
- Expose processEmailItem method in MailingService for individual email processing
- Add comprehensive input schema with conditional fields
- Update plugin to register both tasks and workflows
- Add detailed documentation comparing tasks vs workflows
- Includes status tracking and error handling
- Bump version to 0.3.0 (new feature)

src/types/index.ts

@@ -111,6 +111,7 @@ export interface TemplateVariables {
 
 export interface MailingService {
   processEmails(): Promise<void>
+  processEmailItem(emailId: string): Promise<void>
   retryFailedEmails(): Promise<void>
   renderTemplate(templateSlug: string, variables: TemplateVariables): Promise<{ html: string; text: string; subject: string }>
 }