Create Java multi-module template with Gradle Kotlin DSL and buildSrc

[Copilot]

This PR transforms the repository into a comprehensive Java multi-module template using Gradle with Kotlin DSL, buildSrc, and modern project structure as requested.

What's Added

Project Structure:

• buildSrc/ - Centralized build logic with Kotlin DSL plugins
• gradle/wrapper/ - Gradle wrapper files (version 8.5)
• gradle/libs.versions.toml - Version catalog for dependency management
• modules/ - Multi-module architecture with core and api modules
• src/ - Main application entry point

Build System:

• Gradle Kotlin DSL throughout (all .gradle.kts files)
• java-common.gradle.kts plugin in buildSrc for shared build logic
• Version catalog setup for centralized dependency management
• Java 17 compatibility across all modules

Sample Implementation:

• Core module: Business logic with CoreService class
• API module: External interfaces with ApiController that depends on core
• Main application: Entry point demonstrating module interaction
• Professional logging setup with SLF4J + Logback
• Comprehensive JUnit 5 tests for all modules

Development Experience:

• Type-safe project accessors enabled
• Professional .gitignore for Java/Gradle projects
• Comprehensive README with usage instructions
• All modules build, test, and run successfully

Verification

The template is fully functional:

./gradlew clean build  # ✅ Builds all modules successfully
./gradlew test         # ✅ All tests pass
./gradlew run          # ✅ Application runs with proper logging

This provides a solid foundation for Java projects with modern tooling, clear separation of concerns, and professional project organization.

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