Improve the Empower Plant demo

Improvements for the React Native sample app (Empower Plant demo):

- Remove the custom `UserFeedbackModal` (built-in `feedbackIntegration()` is already active in `App.tsx`)
- Add `hermesProfilingIntegration()` explicitly instead of relying on `profilesSampleRate` alone
- Call `Sentry.appLoaded()` / `reportFullyDisplayed()` to demo standalone app-start + manual TTFD
- Add a "Block JS Thread" button to demo ANR detection (currently on by default but never exercised)
- Configure `networkRequestHeaders` / `networkResponseHeaders` in the existing `mobileReplayIntegration()` init
- Add a rage-tap button (10 rapid taps) to trigger the `ui.multiClick` breadcrumb
- Demo top-level `Sentry.setAttribute` / `setAttributes` (available in v8.17+)
- General cleanup

Already implemented / no longer needed:
- SDK upgrade (currently at 8.19.0)
- `beforeSendTransaction` counterpart to existing `beforeSend`
- `httpClientIntegration()` for non-2xx capture
- `mobileReplayIntegration()` with `networkDetailAllowUrls` and `networkCaptureBodies`

React Native Empower Plant サンプルアプリとそのエントリーポイントである App.tsx から始め、既存の feedbackIntegration() と mobileReplayIntegration() の設定を確認します。列挙された改善を行う前に、現在の profiling、アプリ起動、ANR、replay、breadcrumb、attribute のデモを追跡してください。要求された各動作を実証でき、古いカスタム feedback modal とその他のクリーンアップが削除されていれば完了です。

索引モデルが issue の本文から書いたものです。