feat: add Gradle build with GraalVM Native Image support

[Ryan-Miao]

Summary

• Add Gradle build configuration as an alternative to Maven
• Enable GraalVM Native Image compilation for dramatically improved CLI startup performance
• Use JLine JNI provider for GraalVM compatibility (FFM as runtime fallback)
• Gradle wrapper 9.0.0 with Tencent mirror for China users

Performance Benchmark (Ubuntu, JDK 25.0.2)

Metric	JAR (Maven/Gradle)	Native Image	Improvement
Startup Time	~2500ms	~107ms	23x faster
Memory (RSS)	276 MB	96 MB	65% reduction
Binary Size	72 MB (JAR)	163 MB (native)	Single file, no JRE needed

Usage

# Build JAR (same as Maven)
./gradlew bootJar

# Build native image (requires GraalVM JDK)
./gradlew nativeCompile

# Quick dev build (faster compilation, less optimized)
./gradlew nativeCompile -PquickBuild

# Run
java --enable-preview --enable-native-access=ALL-UNNAMED -jar build/libs/claude-code-java-0.2.0-SNAPSHOT.jar
# or native:
./build/native/nativeCompile/claude-code-java

Files Added/Modified

• build.gradle — Gradle build config with Spring Boot + GraalVM plugin
• settings.gradle — Project name
• gradlew / gradlew.bat — Gradle wrapper scripts
• gradle/wrapper/ — Wrapper jar + properties (Tencent mirror)
• .gitignore — Added Gradle build artifacts

Notes

• Maven is fully preserved — this PR adds Gradle as a parallel option, not a replacement
• GraalVM Native Image requires GraalVM JDK installed (e.g., via SDKMAN: sdk install java 25.0.2-graal)
• Native image is platform-specific — needs to be built on the target OS

Test plan

• ./gradlew bootJar — JAR builds and runs successfully
• ./gradlew nativeCompile — Native image compiles and runs
• Startup benchmark: 2500ms → 107ms
• Memory benchmark: 276MB → 96MB

🤖 Generated with Claude Code