- Add types/api-responses.ts with ApiResponse<T>, PaginatedResponse<T>
- Add types/errors.ts with comprehensive error type hierarchy
- Replace all any usage (53 → 0, 100% reduction)
- Add RawAPI response interfaces for type-safe mapping
- Update catch blocks to use unknown with type narrowing
- Add getState mock to chatStore tests
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>