add CLAUDE.md

Author: ichiroc

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.
+
+## Project Overview
+
+ChatGPT2Scratch is a Scratch extension that enables using OpenAI's ChatGPT (gpt-4o-mini) through Scratch blocks. Hosted on GitHub Pages at `https://ichiroc.github.io/chatgpt2scratch/`.
+
+## Architecture
+
+This repository is an extension that gets installed into scratch-gui — it does not run standalone.
+
+- `scratch-vm/src/extensions/scratch3_chatgpt2scratch/index.js` — Main extension logic: block definitions, OpenAI API calls, i18n (en, ja, ja-Hira)
+- `scratch-gui/src/lib/libraries/extensions/chatgpt2scratch/index.jsx` — Extension entry for the Scratch GUI extension library
+- `install.sh` — Injects the extension into scratch-gui's `node_modules`. Embeds `AZURE_API_KEY` and `DOJO_KEY` environment variables into the source
+
+There is a special code path for access via CoderDojo Japan: it uses an Azure OpenAI endpoint and does not require the user to set an API key.
+
+## Local Development
+
+```sh
+# 1. Clone scratch-gui
+git clone --depth 1 git@github.com:LLK/scratch-gui.git
+cd scratch-gui
+npm install
+
+# 2. Clone this repo and install
+git clone git@github.com:ichiroc/chatgpt2scratch.git
+sh chatgpt2scratch/install.sh
+
+# 3. Start
+npm start
+# Access at http://localhost:8601
+```
+
+## CI/CD
+
+`.github/workflows/build.yml` — Deploys to GitHub Pages on push to main. Checks out scratch-gui, installs the extension, builds, then deploys.