- Add SettingOption StrEnum (nickname/language/timezone) for path param validation - Add UserSettingUpdateRequest DTO with Pydantic constraints - Implement endpoint: extract value by option name, validate non-null for required fields - Fix timezone upper bound from 12 to 14 (UTC+14 exists, e.g. Line Islands) Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>