When switching to custom mode with no templates, show a '+ 新建模板'
button instead of an empty dropdown, allowing users to create the
first template without any UI dead-end.
- Add model config UI in settings panel (local/custom mode)
- local mode: read model names from ~/.claude.json env fields
- custom mode: named templates with API key, base URL, model names
- Fix /compact duplicate message via reason field in pendingCompactRetries
- Add CLAUDE.md with architecture notes
