* handle 3DS challenges on the subscription dashboard
* add `/user/subscription/sync` endpoint
* upgrade `stripe-js` & rm `react-stripe-js`
* group related unit tests together
* add modules `SubscriptionController` unit tests and convert to async/await
* add `StripeClient` unit tests for 3DS failure
GitOrigin-RevId: 9da4758703f6ef4ec08248b328abddbbdd8e44ad