fix: support RN 0.81.5 and below Hermes prefab target on Android

[V3RON]

What is this?

Fixes #216. Apps on React Native 0.81.x failed to configure Voltra's native Android module because packages/android-client/android/CMakeLists.txt hard-coded the RN >= 0.82 Hermes prefab target:

Target "voltra_js_renderer" links to target "hermes-engine::hermesvm" but the target was not found.

RN <= 0.81 publishes the Hermes prefab module as libhermes, exposed to CMake as hermes-engine::libhermes, while RN >= 0.82 uses hermes-engine::hermesvm. This PR makes Voltra support both target names.

The PR also keeps the 16KB page-size alignment fix for libvoltra_js_renderer.so, required for newer Android devices and Play Store submissions.

How does it work?

CMakeLists.txt now probes which Hermes prefab target find_package(hermes-engine) resolved. It links hermes-engine::hermesvm on RN >= 0.82 and hermes-engine::libhermes on RN <= 0.81. If neither target exists, CMake fails early with a Voltra-specific error instead of surfacing a confusing target-link failure later.

libvoltra_js_renderer.so is explicitly linked with -Wl,-z,max-page-size=16384, so the generated native library is 16KB-page-aligned regardless of the NDK version used by the host app. build.gradle also excludes both **/libhermes.so and **/libhermesvm.so, so Voltra does not bundle a duplicate Hermes runtime for either RN generation.

To validate the RN 0.81 path, I generated a fresh React Native CLI app in this repository at test-app-81 with React Native 0.81.0, wired Voltra through local file: dependencies, ran voltra apply --platform android --yes, and built :app:assembleDebug successfully. Then I swapped the same app to published Voltra 2.1.1; the build failed at :use-voltra_android-client:configureCMakeDebug[arm64-v8a] with the missing hermes-engine::hermesvm target. After restoring local file: dependencies, the app built successfully again.

Why is this useful?

This unblocks Voltra Android builds for RN 0.81.x apps, where published 2.1.1 currently fails before native compilation can complete.

It also keeps RN >= 0.82 behavior intact, makes 16KB page-size compliance explicit, and avoids duplicate Hermes .so packaging across both Hermes prefab generations.