Add CLAUDE.md documentation for Claude Code

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CLAUDE.md

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+# 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/