Preload Gradle 9.4.1 in the Android image

[cortinico]

Summary

• preload the Gradle 9.4.1 wrapper distribution in the image
• keep the wrapper cache in /opt/gradle-home, outside the ephemeral GitHub Actions HOME mount
• verify the distribution checksum and retry transient image-build downloads
• verify in CI that React Native's real wrapper starts with container networking disabled

Motivation

React Native job 106382584327 failed before compilation because its fresh container had to download gradle-9.4.1-bin.zip and the wrapper hit its 10-second timeout. The debug matrix sibling downloaded the same distribution successfully and completed, confirming this was a transient network failure rather than a build failure.

Pre-seeding the wrapper cache makes Gradle startup independent of that external download while preserving use of ./gradlew and its version selection.

Test plan

• git diff --check
• Parsed .github/workflows/build.yml with Ruby YAML
• Added a CI check that runs ./gradlew --version with --network none
• Full image build not run locally because no container daemon was active