Add has-many relationship from emails to processing jobs

✨ New Feature:
- Add 'jobs' relationship field to emails collection
- Shows all PayloadCMS jobs associated with each email
- Read-only field with smart filtering by emailId
- Visible in admin interface for better email tracking

🔍 Benefits:
- Track job status and history for each email
- Debug processing issues more easily
- Monitor job queue performance per email
- Complete email processing visibility

src/collections/Emails.ts

@@ -4,7 +4,7 @@ const Emails: CollectionConfig = {
   slug: 'emails',
   admin: {
     useAsTitle: 'subject',
-    defaultColumns: ['subject', 'to', 'status', 'scheduledAt', 'sentAt'],
+    defaultColumns: ['subject', 'to', 'status', 'jobs', 'scheduledAt', 'sentAt'],
     group: 'Mailing',
     description: 'Email delivery and status tracking',
   },
@@ -164,6 +164,24 @@ const Emails: CollectionConfig = {
         description: 'Email priority (1=highest, 10=lowest)',
       },
     },
+    {
+      name: 'jobs',
+      type: 'relationship',
+      relationTo: 'payload-jobs',
+      hasMany: true,
+      admin: {
+        description: 'Processing jobs associated with this email',
+        allowCreate: false,
+        readOnly: true,
+      },
+      filterOptions: ({ id }) => {
+        return {
+          'input.emailId': {
+            equals: id,
+          },
+        }
+      },
+    },
   ],
   timestamps: true,
   // indexes: [