feat(ag-ui): add multi-step wizard interactions

Add a new 'wizard' interaction type to the AG-UI protocol, enabling
agents to present chained, branching prompts to users during execution.

Backend:
- Add WizardStep, WizardField, WizardCondition, WizardDefinition types
- Add WIZARD_STEP_ADVANCE, WIZARD_COMPLETE, WIZARD_CANCELLED events
- Add requestWizard() helper that loops through steps with conditional
  branching and returns aggregated WizardResult
- Update /respond endpoint to accept wizardStepId and wizardCancelled

Frontend:
- Add wizardState to useAgentStream hook with wizard event handling
- Create WizardModal component with stepper progress indicator,
  5 step types (approval, confirm_data, choice, text_input, form),
  conditional step branching, and back/next/cancel navigation
- Glassmorphism styling matching existing InteractionModal

No database migration required — wizard context stored in existing
interaction_context JSONB column. Fully backward compatible.

Author: vincentgrobler

src/components/agui/InteractionModal.tsx

@@ -16,13 +16,14 @@ function formatValue(value: unknown, fallback = '—'): string {
 
 export interface InteractionRequest {
     interactionId: string
-    interactionType: 'approval' | 'confirm_data' | 'choice'
+    interactionType: 'approval' | 'confirm_data' | 'choice' | 'wizard'
     title: string
     description?: string
     data?: Record<string, unknown>
     choices?: { id: string; label: string; description?: string }[]
     timeoutMs: number
     requestedAt: number
+    wizard?: unknown
 }
 
 interface InteractionModalProps {