Match cheap-model trigger label to placeholder hint

The cheap-model dropdown's empty trigger now reflects the same hint
used inside the popover, so the trigger no longer shows "Default" while
the warning copy says the adapter has no default.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

ui/src/components/AgentConfigForm.tsx

@@ -1330,6 +1330,7 @@ function ModelDropdown({
   refreshingModels,
   detectModelLabel,
   emptyDetectHint,
+  defaultLabel,
 }: {
   models: AdapterModel[];
   value: string;
@@ -1347,6 +1348,7 @@ function ModelDropdown({
   refreshingModels?: boolean;
   detectModelLabel?: string;
   emptyDetectHint?: string;
+  defaultLabel?: string;
 }) {
   const [modelSearch, setModelSearch] = useState("");
   const [detectingModel, setDetectingModel] = useState(false);
@@ -1433,7 +1435,8 @@ function ModelDropdown({
             <span className={cn(!value && "text-muted-foreground")}>
               {selected
                 ? selected.label
-                : value || (allowDefault ? "Default" : required ? "Select model (required)" : "Select model")}
+                : value
+                  || (allowDefault ? (defaultLabel ?? "Default") : required ? "Select model (required)" : "Select model")}
             </span>
             <ChevronDown className="h-3 w-3 text-muted-foreground" />
           </button>
@@ -1678,6 +1681,7 @@ function CheapModelSection({
           detectedModel={null}
           detectedModelCandidates={[]}
           emptyDetectHint={placeholderHint}
+          defaultLabel={placeholderHint}
         />
       ) : null}
       {enabled && !model && adapterDefaultModel ? (