Roll back stored settings when a creation fails, and keep form ids unique

create_agent puts back the caps and inference settings it replaced if a
later store or the job insert fails, so a refused creation leaves nothing
behind for the name. The shared field components take an id prefix so the
create dialog and an open editor never share a DOM id. The queue check now
follows the hive roster check, the 422 is documented, and the copy says
empty rather than closed and that destroy keeps stored settings.

frontend/packages/swarm-ui/src/agent/detail/AgentLimits.tsx

@@ -50,16 +50,20 @@ export function LimitsFields({
   memory,
   onCpu,
   onMemory,
+  idPrefix = "limits",
 }: {
   cpu: string;
   memory: string;
   onCpu: (v: string) => void;
   onMemory: (v: string) => void;
+  // Ids must be unique on the page, and the agents page can hold the editor
+  // and the create dialog at once.
+  idPrefix?: string;
 }) {
   return (
     <>
       <TextField
-        id="limits-cpu-quota"
+        id={`${idPrefix}-cpu-quota`}
         label="cpu quota"
         value={cpu}
         placeholder="e.g. 400%"
@@ -69,7 +73,7 @@ export function LimitsFields({
         A percentage of one core: 100% is one core, 400% is four.
       </p>
       <TextField
-        id="limits-memory-max"
+        id={`${idPrefix}-memory-max`}
         label="memory max"
         value={memory}
         placeholder="e.g. 8G"