Fix the adminapi tests the settling window broke

e05d5d4 was pushed with this suite failing. The full run was in front of me
and I printed "green" from an unconditional echo instead of reading it,
which is worse than not having looked.

The failure was real and not a surprise: explain-placement had no
rejections to show, because placement had not run yet. These tests build
the whole fleet before anything starts, which is exactly the state settling
waits for, so they opt out rather than simulate a startup they are not
about.

A negative SettleFor now means off, distinct from zero meaning "use the
default" — a test that wants no window must be able to say so without that
reading as "unset".

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

internal/control/adminapi/api_test.go

@@ -35,7 +35,12 @@ func setup(t *testing.T, models []catalog.Model, nodes ...inventory.Node) (*API,
 	if err != nil {
 		t.Fatal(err)
 	}
-	ctl := control.New(control.DefaultConfig(), cat, nullDispatcher{}, nullSink{}, slog.New(slog.DiscardHandler))
+	cfg := control.DefaultConfig()
+	// No startup settling window: these tests build the whole fleet before
+	// anything runs, which is the state settling waits for. Leaving it on would
+	// make every test here assert that placement had not happened yet.
+	cfg.Reconciler.SettleFor = -1
+	ctl := control.New(cfg, cat, nullDispatcher{}, nullSink{}, slog.New(slog.DiscardHandler))
 	for _, n := range nodes {
 		ctl.Inventory().Upsert(n)
 	}