Migrate Application Validation

application.addHiringTeamMember, application.changeSource, application.changeStage, application.create, application.info, application.list, application.listCriteriaEvaluations, application.listHistory, application.transfer, application.update, and application.updateHistory now return clearer validation errors for malformed request bodies while preserving the existing successful response shapes. The same change applies to the deprecated snake_case aliases application.change_source and application.change_stage, which continue to share validation and behavior with their camelCase counterparts.