Flatten email processing structure to individual jobs per email

BREAKING CHANGE: Replaced batch email processing with individual jobs per email

Changes:
- Remove sendEmailTask.ts - no longer needed as each email gets its own job
- Add processEmailJob.ts - handles individual email processing
- Update sendEmail() to automatically create individual job per email
- Add processImmediately option to sendEmail() for instant processing
- Add processJobById() utility to run specific jobs immediately
- Update job registration to use new individual job structure
- Update dev API routes to use new processImmediately pattern
- Fix all TypeScript compilation errors

Benefits:
- Better job queue visibility (one job per email)
- More granular control over individual email processing
- Easier job monitoring and failure tracking
- Maintains backward compatibility via processImmediately option
- Simpler job queue management

Migration:
- Replace sendEmailJob usage with sendEmail({ processImmediately: true })
- Individual emails now appear as separate jobs in queue
- Batch processing still available via processEmailsTask if needed

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

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

src/jobs/index.ts

@@ -1,14 +1,16 @@
 import { processEmailsJob } from './processEmailsTask.js'
-import { sendEmailJob } from './sendEmailTask.js'
+import { processEmailJob } from './processEmailJob.js'
 
 /**
  * All mailing-related jobs that get registered with Payload
+ *
+ * Note: The sendEmailJob has been removed as each email now gets its own individual processEmailJob
  */
 export const mailingJobs = [
-  processEmailsJob,
-  sendEmailJob,
+  processEmailsJob, // Kept for backward compatibility and batch processing if needed
+  processEmailJob,  // New individual email processing job
 ]
 
 // Re-export everything from individual job files
 export * from './processEmailsTask.js'
-export * from './sendEmailTask.js'
+export * from './processEmailJob.js'