Fix ObjectId casting error when jobs relationship is populated

When the email's jobs relationship is populated with full job objects instead of just IDs,
calling String(job) on an object results in "[object Object]", which causes a Mongoose
ObjectId casting error. This fix properly extracts the ID from job objects or uses the
value directly if it's already an ID.

Fixes job scheduler error: "Cast to ObjectId failed for value '[object Object]'"

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

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

package.json

@@ -1,6 +1,6 @@
 {
   "name": "@xtr-dev/payload-mailing",
-  "version": "0.4.18",
+  "version": "0.4.19",
   "description": "Template-based email system with scheduling and job processing for PayloadCMS",
   "type": "module",
   "main": "dist/index.js",

src/utils/jobScheduler.ts

@@ -129,7 +129,11 @@ export async function updateEmailJobRelationship(
       id: normalizedEmailId,
     })
 
-    const currentJobs = (currentEmail.jobs || []).map((job: any) => String(job))
+    // Extract IDs from job objects or use the value directly if it's already an ID
+    // Jobs can be populated (objects with id field) or just IDs (strings/numbers)
+    const currentJobs = (currentEmail.jobs || []).map((job: any) =>
+      typeof job === 'object' && job !== null && job.id ? String(job.id) : String(job)
+    )
     const allJobs = [...new Set([...currentJobs, ...normalizedJobIds])] // Deduplicate with normalized strings
 
     await payload.update({