fix(client): use section-level dirty tracking instead of form-level isDirty

- Add lastSavedRef and isSectionDirty to useSectionForm hook
- isSectionDirty compares current values against last saved snapshot
  via shallowEqual, immune to server normalization after reconciliation
- CV and Questionnaire wizards: use isSectionDirty in goToStep instead
  of form-level isDirty; remove unnecessary form.reset(form.state.values)
- Employee profile: use isSectionDirty in handleTabChange
- Prevents spurious save-on-tab-switch when server normalises values