swarm-ui: the resource caps dialog says when a change takes effect

The hive reads the caps about every 30 seconds and a running agent takes a
changed cap at its next spawn or rebuild, so the dialog and the ui doc no
longer say the hive applies a change within seconds.

docs/swarm/ui.md

@@ -232,8 +232,12 @@ decides that field again. **clear the swarm's caps** sends the `DELETE`. The
 controller checks each value against systemd's own syntax, because systemd
 ignores a value it can't parse and the agent would run uncapped, and it
 refuses, for example, a percentage with a leading zero. The dialog shows the
-refusal's reason under the fields and leaves them as you typed them. The panel
-reads `GET /api/agents/{agent}/limits`. [hivectl](../tools/hivectl.md#per-agent-resource-limits)
+refusal's reason under the fields and leaves them as you typed them.
+
+A saved change isn't instant. The hive reads the caps about every 30 seconds,
+and a running agent takes a changed cap at its next spawn or rebuild, so the
+row shows the new value before the agent runs under it. The panel reads
+`GET /api/agents/{agent}/limits`. [hivectl](../tools/hivectl.md#per-agent-resource-limits)
 sets the hive's own limits.
 
 ### Linking external accounts

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

@@ -167,7 +167,8 @@ function LimitsForm({
       <p>
         Caps what {agent} may use, wherever it runs. A cap here replaces the
         hive's own answer for that field; an empty box leaves the field to the
-        hive. The hive applies a change within seconds.
+        hive. The hive reads a change within about 30 seconds, and a running
+        agent takes it at its next spawn or rebuild.
       </p>
       <form class="ui-agent-limits-form" onSubmit={save}>
         <TextField