refactor(health): add dashboard overview and related drill-down

- Replace health monitor tabs with a dashboard layout
- Add related health drill-down for endpoint, model, and provider cards
- Render provider health as cards and hide empty monitors

apps/aether-gateway/src/handlers/admin/request/observability.rs

@@ -276,6 +276,26 @@ impl<'a> AdminAppState<'a> {
         .await
     }
 
+    pub(crate) async fn build_related_health_monitor_payload(
+        &self,
+        lookback_hours: u64,
+        dimension: crate::handlers::public::HealthMonitorRelationDimension,
+        value: &str,
+        related_limit: usize,
+        per_item_limit: usize,
+    ) -> Option<serde_json::Value> {
+        crate::handlers::public::build_related_health_monitor_payload(
+            self.app,
+            lookback_hours,
+            dimension,
+            value,
+            related_limit,
+            per_item_limit,
+            true,
+        )
+        .await
+    }
+
     pub(crate) async fn execute_execution_runtime_sync_plan(
         &self,
         trace_id: Option<&str>,