refactor(client): extract useSectionForm hook for multi-section forms

- Create shared useSectionForm hook that handles form, save mutation,
  section reconciliation, and dirty state
- Reconcile only saved section from server response (not full reset)
  to preserve in-progress edits in other sections
- Consume in EmployeeProfileForm, CvWizard, QuestionnaireWizard
- Each consumer passes its own entity type, buildDefaultValues,
  extractSectionData, and saveSection function