Add CLAUDE.md for Claude Code guidance

Add documentation file to help Claude Code understand the Komapper quickstart
project structure, build commands, and architectural patterns. This includes
common Gradle tasks and explains the key concepts like entity annotations,
KSP code generation, and the type-safe query DSL.

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

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

Author: nakamura-to

CLAUDE.md

@@ -0,0 +1,82 @@
+# CLAUDE.md
+
+This file provides guidance to Claude Code (claude.ai/code) when working with code in this repository.
+
+## Commands
+
+### Build and Run
+```bash
+# Run the application
+./gradlew run
+
+# Build the project (compile and test)
+./gradlew build
+
+# Run tests
+./gradlew test
+
+# Run a single test class
+./gradlew test --tests ApplicationTest
+
+# Clean build artifacts
+./gradlew clean
+
+# Compile without running tests
+./gradlew assemble
+```
+
+### Development Commands
+```bash
+# Check code (runs all verification tasks)
+./gradlew check
+
+# Generate KSP code (happens automatically during build)
+./gradlew kspKotlin
+```
+
+## Code Architecture
+
+### Overview
+This is a Komapper quickstart project demonstrating the Komapper ORM framework for Kotlin. Komapper provides type-safe database access with compile-time code generation via KSP (Kotlin Symbol Processing).
+
+### Key Architectural Patterns
+
+1. **Entity Definition with Annotations**
+   - Entities are defined as immutable data classes with Komapper annotations
+   - `@KomapperEntity` marks a class as a database entity
+   - `@KomapperId` with `@KomapperAutoIncrement` for primary keys
+   - `@KomapperVersion` for optimistic locking
+   - `@KomapperCreatedAt`/`@KomapperUpdatedAt` for automatic timestamps
+
+2. **Code Generation via KSP**
+   - KSP generates metamodel classes (e.g., `_Employee`) at compile time
+   - Metamodels provide type-safe property references accessed via `Meta.employee`
+   - No runtime reflection, improving performance
+
+3. **Type-Safe Query DSL**
+   - All database operations use Komapper's type-safe DSL
+   - Queries are built using `QueryDsl` with compile-time verification
+   - Example: `QueryDsl.from(e).where { e.name eq "John" }`
+
+4. **Transaction Management**
+   - Explicit transactions using `database.withTransaction { ... }`
+   - All operations within the block are atomic
+
+### Project Structure
+
+- `src/main/kotlin/org/komapper/quickstart/`
+  - `Application.kt` - Main entry point demonstrating Komapper usage
+  - `Employee.kt` - Entity definition with Komapper annotations
+- `build/generated/ksp/` - Generated metamodel classes (created during build)
+- Database: Uses H2 in-memory database for the example
+
+### Important Technical Details
+
+- **Kotlin Version**: 2.1.21
+- **Komapper Version**: 5.3.0
+- **Target JVM**: Java 11
+- **KSP**: Version 2.1.21-2.0.2 with KSP2 enabled
+- **Testing**: JUnit 5 (Jupiter)
+
+### External Documentation
+For detailed Komapper documentation, refer to: https://www.komapper.org/docs/quickstart/