WP-12: Kubernetes overview and workload actions

kube-rs gateway (nodes, namespaces, deployments/statefulsets/daemonsets with
images, PVCs; rollout restart, scale, set image via patches) using the
microk8s kubeconfig by default, fake gateway for dev, /api/cluster routes,
Kubernetes page with node cards, workload table with admin actions and PVC
list. Also implements the streaming command runner that WP-11 relied on.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

backend/crates/api/src/test_support.rs

@@ -16,6 +16,7 @@ pub fn test_config() -> Config {
         jwt_secret: "test-secret-test-secret-test-secret-1234".into(),
         master_key: "000102030405060708090a0b0c0d0e0f101112131415161718191a1b1c1d1e1f".into(),
         fake_host: true,
+        kubeconfig: None,
         bind: "127.0.0.1:0".parse().unwrap(),
         bootstrap_admin: None,
         cookie_secure: false,
@@ -85,6 +86,7 @@ async fn build_test_app_with(cfg: Config) -> Router {
         Arc::new(RecordingMailer),
         Arc::new(infrastructure::FakeHostInspector),
         Arc::new(infrastructure::FakeHostUpdater),
+        Arc::new(infrastructure::FakeClusterGateway),
         register_test_jobs,
     )
     .expect("state");