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/utils/emailProcessor.ts

@@ -29,6 +29,31 @@ export async function processEmailById(payload: Payload, emailId: string): Promi
   await mailingContext.service.processEmailItem(emailId)
 }
 
+/**
+ * Processes a job immediately by finding and executing it
+ * @param payload Payload instance
+ * @param jobId The ID of the job to run immediately
+ * @returns Promise that resolves when job is processed
+ */
+export async function processJobById(payload: Payload, jobId: string): Promise<void> {
+  if (!payload.jobs) {
+    throw new Error('PayloadCMS jobs not configured - cannot process job immediately')
+  }
+
+  try {
+    // Run a specific job by its ID (using where clause to find the job)
+    await payload.jobs.run({
+      where: {
+        id: {
+          equals: jobId
+        }
+      }
+    })
+  } catch (error) {
+    throw new Error(`Failed to process job ${jobId}: ${error instanceof Error ? error.message : String(error)}`)
+  }
+}
+
 /**
  * Processes all pending and failed emails using the mailing service
  * @param payload Payload instance