V2 UI/UX: linkage search UI, tooltips, workflow stepper and guidance

Implement the UI/UX improvement plan (doc/UI_UX_IMPROVEMENT_PLAN.md).

- Add Tooltip component (keyboard/AT-accessible icon popover) and FormField tip prop
- Add SearchSelect component: debounced async entity picker with loading/empty/
  error states and ARIA combobox behavior
- Add WorkflowStepper component (desktop horizontal / mobile vertical)
- Add ReferenceDataController::searchEntities endpoint (org-scoped) and
  HazardController search support
- Replace raw-ULID hazard linkage on Reports/Show with SearchSelect and add
  disposition radio-cards with descriptions
- Replace raw-ULID linked-item entry on Risks/Show with SearchSelect and render
  the risk workflow stepper
- Add status/band tooltips (StatusBadge, RiskBandBadge) and extend Guide page
  with linkage, workflow-stage, acceptance-routing and effectiveness sections
- Add Hazard/RiskAssessment/RecordRelationship type updates
