feat: Enhance payment event emission and handling

- Updated `emitPaymentEvent` in `PlugpagEventEmitter.kt` to include a custom message parameter for better event logging.
- Refactored `App.tsx` to utilize the new event emission structure, displaying real-time payment event updates.
- Removed deprecated `doPaymentWithEvents` function and integrated its functionality into the standard `doPayment` method.
- Simplified payment flow management by eliminating the `usePaymentFlow` hook.
- Added a new function `generatePixQRCode` for generating PIX QR codes.
- Cleaned up unused styles and components in the UI for better readability and performance.

Author: mCodex