fix: restore E2E APK discovery after AGP 9 migration

[ovitrif]

Why this is required

Before AGP 9, the app build renamed APKs and AABs inside AGP's output directories through applicationVariants, BaseVariantOutputImpl.outputFileName, and FinalizeBundleTask. AGP 9 removes those legacy and internal APIs. There is no supported way to keep writing the established bitkit-* names into AGP's native output directories.

#1127 replaces them with the supported SingleArtifact.APK, SingleArtifact.BUNDLE, and BuiltArtifactsLoader APIs. The resulting artifact-listener tasks run whenever Gradle produces the corresponding app artifact, including direct assemble* and bundle* commands, and publish copies under app/build/outputs/bitkit/<variant>/. Dependent consumers that still search the old AGP paths must update with that producer move.

Producer contract

• Every assemble<Variant> invocation automatically publishes the established versioned bitkit-*.apk copies under app/build/outputs/bitkit/<variant>.
• Every bundle<Variant> invocation automatically publishes the established versioned bitkit-*.aab copy under app/build/outputs/bitkit/<variant>.
• The artifact-listener wiring is the build trigger for these compatibility outputs across direct Gradle commands, Android Studio builds, just commands, and CI.
• Each compatibility directory contains only the current APK or AAB set for its variant.
• AGP's native app-* artifacts and metadata remain owned by AGP under app/build/outputs/apk and app/build/outputs/bundle.

Consumer delivery

Update the two consumers against the AGP 9 producer path. Track both changes through this issue.

• bitkit-e2e-tests/scripts/build-android-apk.sh — fix: locate apk in agp 9 output dir bitkit-e2e-tests#203
  • Resolve exactly one universal APK from app/build/outputs/bitkit/devDebug or app/build/outputs/bitkit/mainnetDebug after the existing assemble* command.
  • Continue writing aut/bitkit_e2e.apk for local and regtest runs.
  • Continue writing aut/bitkit_e2e_mainnet.apk for mainnet runs.
  • Prefer a same-named companion branch as the android PR (chore/agp-9-upgrade) so default E2E branch resolution picks it up.
• bitkit-nightly/.github/workflows/mainnet-probe.yml — synonymdev/bitkit-nightly#45
  • Resolve exactly one universal APK from app/build/outputs/bitkit/mainnetDebug after assembleMainnetDebug.
  • Continue writing and uploading probe-apk/bitkit_e2e.apk.

Consumers hard-cut to the new compatibility directory. A dual-path legacy fallback is not required: the old in-place rename contract cannot be preserved under AGP 9, and coordinating the consumer updates with #1127 is enough.

Delivery order

1. Land the bitkit-e2e-tests compatibility update (fix: locate apk in agp 9 output dir bitkit-e2e-tests#203), ideally on a same-named branch as the android PR until merge.
2. Land the bitkit-nightly compatibility update (synonymdev/bitkit-nightly#45).
3. Merge chore: upgrade to agp 9 and configure parallelism #1127 once in-repo consumers are updated and the external consumer PRs/issues above are ready to land with it.
4. Close this issue after both external consumer paths have run successfully against the merged AGP 9 producer.

Acceptance criteria

• Direct ./gradlew assembleDevDebug publishes exactly one bitkit-dev-debug-*-universal.apk under app/build/outputs/bitkit/devDebug.
• Direct ./gradlew assembleMainnetDebug publishes exactly one bitkit-mainnet-debug-*-universal.apk under app/build/outputs/bitkit/mainnetDebug.
• Direct ./gradlew bundleMainnetRelease publishes exactly one current bitkit-mainnet-release-*.aab under app/build/outputs/bitkit/mainnetRelease.
• The bitkit-e2e-tests Android build helper succeeds against an AGP 9 android ref for local, regtest, and mainnet builds.
• Each E2E helper build writes the expected APK under aut/.
• The bitkit-nightly mainnet probe reaches the upload step with probe-apk/bitkit_e2e.apk present against an AGP 9 android ref.