feat(newsletter): Add comprehensive newsletter management system #157

Job	Run time
Security & Code Quality	1m 26s
Test Suite	52s
Database Tests	1m 4s
Build & Performance	1m 55s
Rollback on Failure	22s
Enhanced Security Testing	-1s
Deploy to Staging	0s
Performance Monitoring (Staging)	0s
Deploy to Production	0s
Performance Monitoring	0s
	5m 38s

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