feat: build subscription SLA monitoring with breach detection

[senmalong]

Summary

Implements subscription SLA monitoring with real-time breach detection, service health evaluation, and credit penalty calculations across backend/services/shared/monitoring.ts, backend/services/monitoring.ts, and src/screens/SlaDashboard.tsx.

Key Changes

• Backend SLA Breach Detector (backend/services/shared/monitoring.ts & backend/services/monitoring.ts):
  • Implemented SlaBreachDetector service for uptime drop detection, latency spike analysis, and error rate surge monitoring.
  • Added automated service credit penalty calculations based on SLA breach severity and uptime drop magnitude.
  • Built compliance report snapshot generator (generateComplianceReport).
• Frontend Dashboard (src/screens/SlaDashboard.tsx):
  • Integrated SLA monitoring snapshot reporting and live breach tracking in the SLA management dashboard.
• Documentation:
  • Added docs/SLA_MONITORING.md covering SLA targets, breach detection rules, and credit penalty formulas.

Closes #957

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[Smartdevs17]

Thanks for contributing! The changes have been merged. Feel free to leave a review or feedback.