Tweak LogBox notifications for iPhone Duo, fix rail touches

[huntie]

Summary

Minimal fixes to the LogBox notification toasts for the iPhone Duo, where they stretch across the unfolded display and block the tab bar beside them when folded.

• Cap the toasts at 600pt wide and center them, so they no longer span the unfolded display edge to edge.
• Fix: Pass touches outside the toasts through to the app, so the folded Duo's rail tab bar beside them stays tappable.
• Fix: Raise the dismiss ×'s contrast from about 2.5:1 to about 7:1. Previously, it drew in the toast's own color on a mid-gray circle and read as faint/invisible; the icon is unchanged.
• Tweak: Round corners from 8 to 12px.

Before	After

Changelog:
[General][Fixed] - LogBox: Fix bottom notification appearance/touch targets on iPhone Duo

Test Plan

yarn test packages/react-native/Libraries/LogBox

iPhone Duo, folded

Before	Before, tab bar blocked	After

✅ With both toasts showing, tapping the rail's APIs tab beside them does nothing before the change and switches tabs after it. Tapping a toast still opens the inspector.

iPhone Duo, unfolded

Before	After

✅ The toasts span the display before the change and are capped and centered after it.

[meta-codesync]

@Abbondanzo has imported this pull request. If you are a Meta employee, you can view this in D124115690.

[meta-codesync]

@Abbondanzo merged this pull request in 88a8bd2.