swarm-ui: use ConfirmDialog for the stop confirmation too

mara: "use the new component where we already have confirm dialogs."
The stop/offline direction of the wanted toggle used a native
window.confirm -- the reasoning at the time was that a hand-rolled
Dialog felt heavy for a reversible action, with the real Dialog confirm
reserved for the irreversible destroy direction. Now that
ConfirmDialog is a one-line-per-caller shared component, that argument
no longer buys consistency anything, so both directions confirm the
same way.

frontend/packages/swarm-ui/src/pages/AgentsPage.tsx

@@ -25,9 +25,9 @@
 // itself (`CreateAgentForm`) mounts inside a `Dialog` here rather than
 // its own route.
 //
-// The "wanted" column is the start/stop control — see its own `render`
-// and `toggleWanted` below for how. Destroy is a separate control next
-// to it — see `destroyTarget`/`destroyAgent`.
+// The "wanted" column is the start/stop control (`toggleWanted`) plus a
+// separate destroy control (`destroyAgent`) — both confirm via the
+// shared `ui/confirm-dialog`.
 import { useState } from "preact/hooks";
 import { ApiErrorPanel } from "@hive/shared/api-error-panel.js";
 import { readApiError, type ProblemDetails } from "@hive/shared/api-error.js";
@@ -119,8 +119,13 @@ export function AgentsPage() {
   >(new Map());
   // The row pending destroy confirmation, `null` when the dialog is
   // closed — not a boolean, so the dialog can name the agent without a
-  // second piece of state to keep in sync with it.
+  // second piece of state to keep in sync with it. `stopTarget` mirrors
+  // it for the "declare offline" direction of the same toggle — two
+  // separate pieces of state (not one "pending confirm" union) since
+  // both `ConfirmDialog`s can't be open at once anyway and keeping them
+  // apart means each one's JSX below reads standalone.
   const [destroyTarget, setDestroyTarget] = useState<AgentRow | null>(null);
+  const [stopTarget, setStopTarget] = useState<AgentRow | null>(null);
 
   async function refresh() {
     const res = await fetch("/api/agents/status");
@@ -139,11 +144,11 @@ export function AgentsPage() {
     refresh().catch((e: unknown) => setError({ detail: String(e) }));
   });
 
-  // Shared by `toggleWanted` and `destroyAgent` — both are "PUT a new
+  // Shared by `confirmStop` and `destroyAgent` — both are "PUT a new
   // `wanted` declaration, track per-agent pending/error state, patch the
   // response back into `rows`" with nothing else distinguishing them.
-  // Confirmation (native vs. `Dialog`) and target-state selection stay
-  // in each caller, since those are the parts that actually differ.
+  // Which `ConfirmDialog` fires it and the target state stay in each
+  // caller, since those are the parts that actually differ.
   async function declareState(row: AgentRow, target: string) {
     if (!row.hive) return;
     setPendingAgents((prev) => new Set(prev).add(row.name));
@@ -201,31 +206,38 @@ export function AgentsPage() {
   // target is read off the agent's own last-reported `running` instead
   // — the button's first click always means "make the declaration match
   // reality, then flip it", which is the only reading that makes sense
-  // without a declaration to toggle.
+  // without a declaration to toggle. The "up" direction needs no
+  // confirmation and declares straight away; "offline" opens the
+  // `stopTarget` `ConfirmDialog` instead of declaring directly — see
+  // `confirmStop`.
   async function toggleWanted(row: AgentRow) {
     if (!row.hive) return;
     const impliedCurrent =
       row.wanted ?? (row.snapshot?.running ? "up" : "offline");
     const target = impliedCurrent === "up" ? "offline" : "up";
-    if (
-      target === "offline" &&
-      // Native confirm, not a `Dialog` — stop is reversible (a later
-      // start un-does it), so the lighter-weight native prompt is
-      // proportionate here. Destroy is the irreversible direction and
-      // gets the real `Dialog` confirm instead — see `destroyAgent`.
-      !window.confirm(
-        `Declare ${row.name} offline? The hive brings its container down on its next reconcile sweep.`,
-      )
-    ) {
+    if (target === "offline") {
+      setStopTarget(row);
       return;
     }
     await declareState(row, target);
   }
 
-  // Fires from the confirm `Dialog`, never directly off a row click —
-  // see `destroyTarget`/the "destroy" badge in the `wanted` column.
-  // Unlike `toggleWanted`, there's no "current state" to read: destroy
-  // is a one-way declaration, not a flip.
+  // Fires from the `stopTarget` confirm `Dialog`. Used to be a native
+  // `window.confirm` (stop is reversible, a later start un-does it, so a
+  // lighter-weight prompt than destroy's felt proportionate) — mara,
+  // reviewing the destroy confirm: use the shared component everywhere
+  // we already confirm before acting, not just for destroy. Once
+  // `ConfirmDialog` existed as a one-line-per-caller component, the
+  // "native is lighter" argument no longer bought consistency anything.
+  async function confirmStop(row: AgentRow) {
+    setStopTarget(null);
+    await declareState(row, "offline");
+  }
+
+  // Fires from the `destroyTarget` confirm `Dialog`, never directly off
+  // a row click — see `destroyTarget`/the "destroy" badge in the
+  // `wanted` column. Unlike `toggleWanted`, there's no "current state"
+  // to read: destroy is a one-way declaration, not a flip.
   async function destroyAgent(row: AgentRow) {
     setDestroyTarget(null);
     await declareState(row, "destroyed");
@@ -415,6 +427,20 @@ export function AgentsPage() {
       >
         <CreateAgentForm />
       </Dialog>
+      <ConfirmDialog
+        open={stopTarget !== null}
+        label="stop agent"
+        onCancel={() => setStopTarget(null)}
+        onConfirm={() => stopTarget && void confirmStop(stopTarget)}
+        confirmLabel="stop"
+      >
+        {stopTarget ? (
+          <p>
+            Declare <strong>{stopTarget.name}</strong> offline? The hive brings
+            its container down on its next reconcile sweep.
+          </p>
+        ) : null}
+      </ConfirmDialog>
       <ConfirmDialog
         open={destroyTarget !== null}
         label="destroy agent"