feat(openclaw): add default model button and fix sessionsApi export

- Add "Enable as Default" button to OpenClaw provider cards
- Place enable button before add/remove button for better UX
- Disable remove button when provider is set as default
- Add sessionsApi re-export from api barrel file to fix white screen
- Add i18n keys for default model feature (zh/en/ja)

src/components/providers/ProviderCard.tsx

@@ -48,6 +48,9 @@ interface ProviderCardProps {
   isInFailoverQueue?: boolean; // 是否在故障转移队列中
   onToggleFailover?: (enabled: boolean) => void; // 切换故障转移队列
   activeProviderId?: string; // 代理当前实际使用的供应商 ID（用于故障转移模式下标注绿色边框）
+  // OpenClaw: default model
+  isDefaultModel?: boolean;
+  onSetAsDefault?: () => void;
 }
 
 const extractApiUrl = (provider: Provider, fallbackText: string) => {
@@ -108,6 +111,9 @@ export function ProviderCard({
   isInFailoverQueue = false,
   onToggleFailover,
   activeProviderId,
+  // OpenClaw: default model
+  isDefaultModel,
+  onSetAsDefault,
 }: ProviderCardProps) {
   const { t } = useTranslation();
 
@@ -386,6 +392,9 @@ export function ProviderCard({
               isAutoFailoverEnabled={isAutoFailoverEnabled}
               isInFailoverQueue={isInFailoverQueue}
               onToggleFailover={onToggleFailover}
+              // OpenClaw: default model
+              isDefaultModel={isDefaultModel}
+              onSetAsDefault={onSetAsDefault}
             />
           </div>
         </div>