docs: document Android edge-to-edge setup

[huytdps13400]

Summary

• document the React Native edgeToEdgeEnabled setup for Android display cutouts
• explain the fallback for custom activities, fragments, and older React Native versions
• show safe-area inset consumption and replace legacy FLAG_LAYOUT_NO_LIMITS guidance
• call out Android 15 cutout behavior and portrait/landscape cutout testing

Fixes #216

Verification

• yarn build in docs
• yarn typecheck in docs
• Prettier check for docs/docs/usage.mdx
• root Prettier and clang format checks
• task-local ./gradlew spotlessCheck
• yarn validate:eslint (0 errors; 3 existing deep-import warnings)
• yarn validate:typescript
• yarn validate:jest (4 suites, 21 tests, 11 snapshots)

References

• Android edge-to-edge and display-cutout documentation
• React Native 0.81 Android 16/edge-to-edge guidance

Screenshots

Not applicable — documentation-only change.