🚧 Add broker status page

backend/app/routers/broker.py

@@ -33,6 +33,7 @@ from app.models import (
 from app.schemas import (
     BrokerSettingsIn,
     BrokerSettingsOut,
+    BrokerStatusOut,
     ConfigPreviewOut,
     DeployRequest,
     ListenerIn,
@@ -316,6 +317,19 @@ def _publish_certificates(db: Session) -> None:
                 )
 
 
+@router.get("/status", response_model=BrokerStatusOut)
+def broker_status(_user: AnyReader):
+    """Live $SYS telemetry for the dashboard (spec sections 33, 55).
+
+    Read-only: every management role may view (spec section 9). Fields
+    are None until the first $SYS publish arrives — the broker publishes
+    on sys_interval (10 s), so a fresh backend needs a few seconds.
+    """
+    from app import metrics
+
+    return BrokerStatusOut(**metrics.snapshot())
+
+
 @router.get("/config/preview", response_model=ConfigPreviewOut)
 def preview_config(
     db: Annotated[Session, Depends(get_db)], _user: AnyReader