Improve the Empower Plant demo

[alwx]

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

[linear-code]

RN-718

[sentry-pierre]

I cleaned up the list after checking the current sample app on main. A few items were already in place:

• The SDK is at 8.19.0.
• beforeSendTransaction, httpClientIntegration(), and feedbackIntegration() are already wired in App.tsx.
• mobileReplayIntegration() already configures networkDetailAllowUrls and networkCaptureBodies.

A maintainer can pick the remaining slices from here.