Feat/add system notificaton services

[Rashed99Azm]

Summary

• Refactored notification system with a base EntityRepository<T, TId> pattern and replaced all notification repos to extend it
• Integrated password reset into the notification pipeline with Email+SMS delivery, bypassing user opt-out for security alerts
• Replaced MarkAllRead raw SQL with DDD-compliant domain-method calls; deleted unused IPasswordResetEmailSender/PasswordResetEmailSender and dead IsUserSuppressedAsync method
  Test plan
• dotnet test backend/CCE.sln green
• pnpm nx run-many -t lint,test green (N/A — monorepo frontend not in this PR scope)
• If API surface changed: ./scripts/check-contracts-clean.sh green (N/A — no contract changes)
• If UI changed: pnpm nx run-many -t e2e (N/A — backend-only PR)
• Manual smoke notes: Seeder runs idempotently with --demo and --migrate --seed-reference; password reset flow dispatches via gateway on both Email and SMS channels
  Security checklist
• No new secrets / credentials in code
• AuthN / AuthZ impact considered — ForgotPasswordAsync still returns 200 OK regardless of result (no user enumeration)
• Input validation on new endpoints — no new endpoints
• Audit-log entry for new state-changing operations — notification logs are created for password reset dispatches via the existing NotificationLog mechanism