## Summary
- Add comprehensive test suite for `readSettings()` covering all setting
types including nested objects
- Refactor `UserSettings` schema using Zod with proper nested objects
(`chatMode.enabled`, `chatMode.mode`, `thinking.enabled`,
`thinking.budget`)
- Add migration path for legacy flat settings format to new nested
structure

## Test plan
- Run `npm test` to verify all 814 tests pass including new readSettings
tests
- Verify settings are properly loaded with both new nested format and
legacy flat format

🤖 Generated with [Claude Code](https://claude.com/claude-code)
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---------
Co-authored-by: Will Chen <willchen90@gmail.com>
Co-authored-by: Claude Opus 4.5 <noreply@anthropic.com>
Co-authored-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com>