feat: publish io.parity:truapi-host as an AAR

[valentinfernandez1]

Closes #328.
Related https://github.com/paritytech/polkadot-app-android-v2/pull/953

What

truapi now publishes the Android host as io.parity:truapi-host on GitHub Packages. The AAR bundles the per-ABI libtruapi_server.so (arm64-v8a, armeabi-v7a, x86, x86_64), the UniFFI Kotlin bindings, and the Kotlin shell, all built from the same source. Consumers only need Gradle. JNA is the only runtime dependency.

What changed

• release-android workflow: builds and publishes the AAR on a truapi-host-android@<version> tag or a manual run.
• ci-android workflow: compiles the shell against fresh bindings on PRs touching android/ or the native crates.
• make android-jni now covers all four ABIs and removes stray dependency .so files, so the AAR carries exactly four libtruapi_server.so.
• Coordinates renamed to io.parity:truapi-host, version comes from -PtruapiHostVersion.
• New review-fixtures bin in truapi-platform prints canonical SCALE hex per UserConfirmationReview variant, with a golden test that fails on any encoding drift.
• READMEs updated for consuming, releasing, and fixture regeneration.

Draft: verifying the publish from this branch

workflow_dispatch only works once the workflow file is on the default branch, so this PR carries a temporary push trigger on this branch. Every push publishes 0.1.0-rc.<run number> to GitHub Packages, which lets us prove the whole pipeline before merging. Before marking ready for review: remove the temporary trigger and delete the rc packages from the registry.

Once the pipeline is proven, a follow-up will fold the Android publish into the normal release: commit flow so it is not a separate step people can forget.