chore: add CLAUDE.md and gitignore package-lock.json

Enforce pnpm usage for AI agents and prevent stray npm lock files.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

.gitignore

@@ -13,6 +13,7 @@ release/
 
 # pnpm
 .pnpm-store/
+package-lock.json
 
 # Environment
 .env

CLAUDE.md

@@ -0,0 +1,10 @@
+# CLAUDE.md
+
+## Package Manager
+
+This project uses **pnpm**. Never use `npm` or `yarn`.
+
+- Use `pnpm install` (not `npm install`)
+- Use `pnpm add <pkg>` (not `npm install <pkg>`)
+- Use `pnpm run <script>` (not `npm run <script>`)
+- The lock file is `pnpm-lock.yaml`. Do not generate `package-lock.json` or `yarn.lock`.