feat: SAC 0.7.4 sidebar system stats block with UI toggle

Co-authored-by: Cursor <cursoragent@cursor.com>

backend/app/models/__init__.py

@@ -6,6 +6,7 @@ from app.models.notification_cooldown import NotificationCooldown
 from app.models.notification_policy import NotificationPolicy
 from app.models.problem import Problem, ProblemEvent
 from app.models.login_attempt import LoginAttempt
+from app.models.ui_settings import UiSettings
 from app.models.event_severity_override import EventSeverityOverride
 from app.models.user import User
 
@@ -21,4 +22,5 @@ __all__ = [
     "User",
     "EventSeverityOverride",
     "LoginAttempt",
+    "UiSettings",
 ]