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/openapi.rs

@@ -27,6 +27,7 @@ impl Modify for BearerAuth {
         crate::settings::get_smtp, crate::settings::put_smtp, crate::settings::test_smtp, crate::settings::list_schedules, crate::settings::put_schedule,
         crate::jobs::list, crate::jobs::kinds, crate::jobs::get_one, crate::jobs::run,
         crate::system::inventory, crate::system::upgrade,
+        crate::cluster::overview, crate::cluster::restart, crate::cluster::scale, crate::cluster::set_image,
     ),
     modifiers(&BearerAuth)
 )]