Fix error handling and improve naming consistency

- Use native error chaining in workflow (Error constructor with cause option)
- Fix job scheduling to use 'task' instead of 'workflow' property
- Rename processEmailsJob.ts to processEmailsTask.ts for consistency
- Update all imports and references while maintaining backward compatibility
- Add processEmailsTask export with processEmailsJob alias
- Bump version to 0.3.1

package.json

@@ -1,6 +1,6 @@
 {
   "name": "@xtr-dev/payload-mailing",
-  "version": "0.3.0",
+  "version": "0.3.1",
   "description": "Template-based email system with scheduling and job processing for PayloadCMS",
   "type": "module",
   "main": "dist/index.js",