Add rollback ratio alert tuning parameters

Introduced new parameters to fine-tune rollback ratio alerts and reduce false positives on low-traffic databases. Adjusted evaluation logic to account for minimum rollback counts and transaction volumes, ensuring more reliable alert thresholds. Updated .env.example and descriptions for better configuration clarity.

backend/app/core/config.py

@@ -26,6 +26,9 @@ class Settings(BaseSettings):
     cors_origins: str = "http://localhost:5173"
     poll_interval_seconds: int = 30
     alert_active_connection_ratio_min_total_connections: int = 5
+    alert_rollback_ratio_window_minutes: int = 15
+    alert_rollback_ratio_min_total_transactions: int = 100
+    alert_rollback_ratio_min_rollbacks: int = 10
     init_admin_email: str = "admin@example.com"
     init_admin_password: str = "ChangeMe123!"