Java 8 to 11 Migration: Toolchain Configuration and CI Updates

[devin-ai-integration]

Summary

This PR improves the Java 11 build configuration by adding proper Gradle toolchain support and modernizing the CI workflow. The project was already targeting Java 11 but lacked explicit toolchain configuration and had outdated CI action versions.

Build changes:

• Added Java toolchain configuration in build.gradle (replaces sourceCompatibility/targetCompatibility)
• Upgraded Gradle wrapper from 7.4 to 7.6.4
• Upgraded Spotless plugin from 6.2.1 to 6.25.0 (required for Java 11+ module system compatibility)
• Added UTF-8 encoding for Java compilation

CI changes:

• Updated GitHub Actions to v4 (checkout, setup-java)
• Changed JDK distribution from Zulu to Temurin
• Simplified caching using setup-java's built-in Gradle cache support

Review & Testing Checklist for Human

• Verify CI passes with the updated workflow and Gradle configuration
• Confirm the Spotless plugin upgrade (6.2.1 → 6.25.0) doesn't introduce unexpected formatting changes beyond the one file modified (DefaultJwtServiceTest.java)
• Validate that the toolchain configuration produces Java 11 bytecode (can check with javap -v on a compiled class)

Recommended test plan: After CI passes, pull the branch locally and run ./gradlew clean build test to verify the build works end-to-end.

Notes

The codebase was analyzed for usage of removed JDK modules (JAXB, JAX-WS, JavaFX, CORBA, Nashorn) - none were found, so no additional dependencies were needed.

See MIGRATION_NOTES.md for detailed documentation of all changes.

Link to Devin run: https://app.devin.ai/sessions/22a134aac3e944e9a8ca4a321fa2f16f
Requested by: milind@cognition.ai (@milind-cognition)

[devin-ai-integration]

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