fix(docker): enhance error handling and user feedback for Docker service unavailability

frontend/src/hooks/useDocker.ts

@@ -9,7 +9,19 @@ export function useDocker(host?: string | null, serverId?: string | null) {
     refetch,
   } = useQuery({
     queryKey: ['docker-containers', host, serverId],
-    queryFn: () => dockerApi.listContainers(host || undefined, serverId || undefined),
+    queryFn: async () => {
+      try {
+        return await dockerApi.listContainers(host || undefined, serverId || undefined)
+      } catch (err: any) {
+        // Extract helpful error message from response
+        if (err.response?.status === 503) {
+          const details = err.response?.data?.details
+          const message = details || 'Docker service unavailable. Check that Docker is running.'
+          throw new Error(message)
+        }
+        throw err
+      }
+    },
     enabled: Boolean(host) || Boolean(serverId),
     retry: 1, // Don't retry too much if docker is not available
   })