docs: add CLAUDE.md with project structure and development commands

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

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

Author: koki-develop

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.
+
+## Common Commands
+
+- **Build**: `bun run build` - Uses the custom build script in `scripts/build.ts`
+- **Lint**: `bun run lint` - Runs Biome linter checks
+- **Format**: `bun run fmt` - Formats code using Biome with unsafe fixes
+- **Type check**: `bun run typecheck` - Runs TypeScript compiler without emitting files
+
+## Project Structure
+
+This is a TypeScript CLI tool using the following stack:
+- **Runtime**: Bun (primary development runtime)
+- **CLI Framework**: Commander.js for argument parsing
+- **Build Tool**: Custom Bun build script that creates executable CLI binary
+- **Linting/Formatting**: Biome (replaces ESLint + Prettier)
+- **Package Manager**: Bun with lockfile management
+
+### Key Files
+- `src/index.ts` - Main entry point with Commander.js CLI setup
+- `scripts/build.ts` - Custom build script that outputs to `dist/` with shebang
+- `biome.json` - Biome configuration for linting and formatting
+- `tsconfig.json` - TypeScript configuration optimized for bundler mode
+
+### Build Process
+The build process creates a standalone executable CLI tool:
+1. Removes existing `dist/` directory
+2. Uses Bun.build() to bundle TypeScript to JavaScript
+3. Adds Node.js shebang for CLI execution
+4. Makes output executable with chmod +x
+
+## Development Notes
+
+- Uses `"module": "Preserve"` and `"moduleResolution": "bundler"` in tsconfig for modern bundler compatibility
+- Biome is configured with strict rules including unused variable/import detection
+- Package is configured as ESM with `"type": "module"`
+- Binary is published as `cat-code` command via `bin` field in package.json