feat: add claude.md

Author: ryoppippi

CLAUDE.md

@@ -0,0 +1,48 @@
+# CLAUDE.md
+
+This file provides guidance to Claude Code (claude.ai/code) when working with code in this repository.
+
+## Development Commands
+
+**Testing and Quality:**
+- `bun test` - Run all tests
+- `bun run lint` - Lint code with Biome
+- `bun run format` - Format code with Biome (writes changes)
+- `bun typecheck` - Type check with TypeScript (note: script name has typo "typecheek")
+
+**Build and Release:**
+- `bun run build` - Build distribution files with tsdown
+- `bun run release` - Full release workflow (lint + typecheck + test + build + version bump)
+
+**Development Usage:**
+- `bun run report daily` - Show daily usage report
+- `bun run report session` - Show session-based usage report
+- `bun run index.ts` - Direct execution for development
+
+## Architecture Overview
+
+This is a CLI tool that analyzes Claude Code usage data from local JSONL files stored in `~/.claude/projects/`. The architecture follows a clear separation of concerns:
+
+**Core Data Flow:**
+1. **Data Loading** (`data-loader.ts`) - Parses JSONL files from Claude's local storage
+2. **Cost Calculation** (`cost-calculator.ts`) - Handles token-to-cost conversions using LiteLLM pricing data
+3. **Command Execution** (`commands/`) - CLI subcommands that orchestrate data loading and presentation
+4. **CLI Entry** (`index.ts`) - Gunshi-based CLI setup with subcommand routing
+
+**Key Data Structures:**
+- Raw usage data is parsed from JSONL with timestamp, token counts, and pre-calculated costs
+- Data is aggregated into either daily summaries or session summaries
+- Sessions are identified by directory structure: `projects/{project}/{session}/{file}.jsonl`
+
+**External Dependencies:**
+- Uses LiteLLM model pricing data for cost calculations (JSON format in `model_prices.json`)
+- Supports JST timezone conversion for date formatting
+- CLI built with `gunshi` framework, tables with `cli-table3`
+
+## Code Style Notes
+
+- Uses Biome for formatting with tab indentation and double quotes
+- TypeScript with strict mode and bundler module resolution
+- No console.log allowed except where explicitly disabled with biome-ignore
+- Error handling: silently skips malformed JSONL lines during parsing
+- File paths always use Node.js path utilities for cross-platform compatibility