Add CLAUDE.md for Claude Code guidance (#672)

* Add CLAUDE.md for Claude Code guidance

This file provides essential guidance for Claude Code when working with
the snappy-java repository, including:
- Common build and test commands
- High-level architecture overview
- Platform support details
- Important implementation notes

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <[email protected]>

* Remove outdated findbugs and jacoco commands

* Fix test command for debug logging

* Clarify test frameworks: AirSpec for Scala, JUnit for Java

---------

Co-authored-by: Claude <[email protected]>

Author: xerial

CLAUDE.md

@@ -0,0 +1,101 @@
+# CLAUDE.md
+
+This file provides guidance to Claude Code (claude.ai/code) when working with code in this repository.
+
+## Project Overview
+
+snappy-java is a Java port of Google's Snappy compression library, providing fast compression/decompression with JNI bindings for native performance across multiple platforms.
+
+## Build Commands
+
+### Using sbt (primary build tool)
+
+```bash
+# Enter sbt console
+./sbt
+
+# Run tests
+./sbt test
+
+# Run tests matching a pattern
+./sbt "testOnly *BitShuffleTest"
+
+# Create jar file
+./sbt package
+
+# Publish to local Maven repository
+./sbt publishM2
+
+# Run tests continuously on code changes
+./sbt "~test"
+```
+
+### Using make (for native library compilation)
+
+```bash
+# Build native libraries
+make
+
+# Clean build artifacts
+make clean
+
+# Platform-specific builds (when cross-compiling)
+make native-all
+```
+
+## Architecture
+
+### Core Components
+
+1. **Java API Layer** (`src/main/java/org/xerial/snappy/`)
+   - `Snappy.java`: Main API facade providing high-level compression/decompression methods
+   - `SnappyNative.java`: JNI interface to native Snappy library
+   - `SnappyLoader.java`: Handles platform-specific native library loading
+
+2. **Native Layer** (`src/main/java/org/xerial/snappy/`)
+   - `SnappyNative.cpp`: JNI implementation bridging Java and C++ Snappy
+   - `BitShuffleNative.cpp`: JNI implementation for BitShuffle algorithm
+
+3. **Stream API** (`src/main/java/org/xerial/snappy/`)
+   - `SnappyOutputStream`/`SnappyInputStream`: Block-based compression streams
+   - `SnappyFramedOutputStream`/`SnappyFramedInputStream`: Framing format implementation
+   - `SnappyHadoopCompatibleOutputStream`: Hadoop-compatible format
+
+4. **Memory Management** (`src/main/java/org/xerial/snappy/buffer/` and `/pool/`)
+   - Buffer allocation and pooling for efficient memory usage
+   - Direct ByteBuffer management for zero-copy operations
+
+### Platform Support
+
+The project includes pre-built native libraries for multiple platforms in `src/main/resources/org/xerial/snappy/native/`:
+- Windows (x86, x86_64, aarch64)
+- macOS (x86, x86_64, aarch64)
+- Linux (x86, x86_64, aarch64, arm, armv6, armv7, ppc64, ppc64le, s390x, riscv64, loongarch64)
+- AIX (ppc, ppc64)
+- SunOS (x86, x86_64, sparc)
+- Android (arm, aarch64)
+
+### Cross-compilation
+
+The project uses Docker-based cross-compilation toolchains (see `docker/` directory) for building native libraries across different architectures.
+
+## Testing
+
+```bash
+# Run all tests with debug logging
+./sbt "testOnly * -- -l debug"
+
+# Run specific test class
+./sbt "testOnly org.xerial.snappy.SnappyTest"
+
+# The project uses AirSpec (for Scala tests) and JUnit (for Java tests)
+# Tests are located in src/test/java/org/xerial/snappy/
+```
+
+## Important Notes
+
+1. **Native Library Loading**: The project automatically detects the platform and loads the appropriate native library from resources
+2. **Memory Safety**: Uses direct ByteBuffers for efficient memory operations - be aware of buffer boundaries
+3. **Thread Safety**: Snappy compression/decompression methods are thread-safe as they don't maintain state
+4. **OSGi Support**: The project includes OSGi bundle configuration in build.sbt
+5. **Compatibility**: Multiple stream formats are supported - ensure you use matching read/write formats (see compatibility matrix in README.md)