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/lib/query/mutations.ts

@@ -187,6 +187,9 @@ export const useSwitchProviderMutation = (appId: AppId) => {
         await queryClient.invalidateQueries({
           queryKey: ["openclawLiveProviderIds"],
         });
+        await queryClient.invalidateQueries({
+          queryKey: ["openclawDefaultModel"],
+        });
       }
 
       try {