CI: Add GitHub Actions workflow to build Android library

[jihanurrahman33]

This PR introduces a minimal GitHub Actions workflow that:

• Sets up JDK 17 and Android SDK (API 34, build-tools 34.0.0)
• Caches Gradle via gradle/actions/setup-gradle
• Builds the library module (:veridui:assemble) and runs unit tests (:veridui:test)

Rationale:

• Provides automated verification for PRs and pushes
• Aligns with current project configuration (AGP 8.x, Java 17)
• Keeps scope small and non-invasive; no changes to code

Future follow-ups could add lint checks and build the sample module if desired.