chore(android): align Android Gradle Plugin at 9.3.1

[CodeinScrubs]

Summary

• update both root Android application/library plugin pins to AGP 9.3.1
• update the standalone Maven consumer smoke project to the same AGP version
• keep all Android builds on the verified Gradle 9.6.1 wrapper and JDK 21 matrix

This combines and supersedes Dependabot PRs #19 and #22 so application, library, and isolated-consumer validation cannot drift between AGP versions.

Local verification

• core/views/compose unit tests
• release lint for all libraries and debug lint for the sample
• release AARs, sample APK, and Maven-local publication
• isolated consumer clean build against Maven coordinates
• --warning-mode all consumer build with the former Gradle 10 project-notation warning eliminated
• git diff --check