feat: add dual architecture support (Fabric & Paper) via Legacy Interop

[theashraf]

Summary

• add Fabric component view and provider on iOS behind RCT_NEW_ARCH_ENABLED, keeping existing Paper manager as default
• enable Android legacy interop so the view works in both architectures, plus Gradle toggles/scripts to flip newArchEnabled
• refresh the example app (cleanup generated files, new yarn tasks, updated iOS project) so it can build/run in Paper or Fabric modes
• document architecture toggles in the main README

Testing

• yarn ios:paper
• yarn ios:fabric
• yarn android:paper
• yarn android:fabric

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