Where do slash-commands live, and do they sync across machines?

Two scopes. Project: .claude/commands/<name>.md, commits with your repo, syncs to teammates via git. User: ~/.claude/commands/<name>.md, only on your laptop. The file is plain Markdown with optional YAML frontmatter for argument hints. Project commands win on name collisions. Rule of thumb: anything Magento-specific (/scaffold-feature, /add-graphql) goes in the project; anything personal (/explain-this, /summarise) goes in user. Don't put secrets in either, commands are plain text and end up in the prompt.