feat: SSH card UX, agent version sync, persistent ssh_admin_ok (0.11.5)

Silent SSH probe on host card open; manual test feedback auto-hides. Persist ssh_admin_ok in DB (migration 019). After agent update read version from host and refresh UI.

frontend/src/utils/hostPatchBus.ts

@@ -0,0 +1,16 @@
+import type { HostDetail } from "../api";
+
+type HostPatchListener = (detail: HostDetail) => void;
+
+const listeners = new Set<HostPatchListener>();
+
+export function subscribeHostPatch(listener: HostPatchListener): () => void {
+  listeners.add(listener);
+  return () => listeners.delete(listener);
+}
+
+export function emitHostPatch(detail: HostDetail): void {
+  for (const listener of listeners) {
+    listener(detail);
+  }
+}