feat: add router health metrics to node_cache and node-guardian

- Add migration 042_node_cache_router_metrics.sql
- Node guardian now collects router health and sends in heartbeat
- City-service uses cached router_healthy from node_cache
- This allows NODE2 router status to be displayed correctly

services/city-service/repo_city.py

@@ -3373,7 +3373,7 @@ async def get_node_endpoints(node_id: str) -> Dict[str, str]:
 
 async def get_node_metrics(node_id: str) -> Optional[Dict[str, Any]]:
     """
-    Отримати розширені метрики ноди (включаючи Swapper).
+    Отримати розширені метрики ноди (включаючи Swapper та Router).
     """
     pool = await get_pool()
     
@@ -3385,7 +3385,9 @@ async def get_node_metrics(node_id: str) -> Optional[Dict[str, Any]]:
             swapper_models_total,
             swapper_state,
             router_url,
-            swapper_url
+            swapper_url,
+            router_healthy,
+            router_version
         FROM node_cache
         WHERE node_id = $1
     """, node_id)