CartButton molecule + progress bar on all wizard layouts

- New CartButton molecule: outlined pill trigger with receipt icon,
  "Your Plan" label + formatted total in brand colour. Click opens
  DialogShell with items grouped by section via LineItem, total row,
  empty state. Mobile collapses to icon + price.
- WizardLayout: remove STEPPER_VARIANTS whitelist — stepper bar now
  renders on any layout variant when progressStepper/runningTotal props
  are provided (StepperBar already returns null when both empty)
- Thread progressStepper + runningTotal props to DateTimeStep, VenueStep,
  SummaryStep, PaymentStep (joins 8 pages that already had them)

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/components/pages/VenueStep/VenueStep.tsx

@@ -52,6 +52,10 @@ export interface VenueStepProps {
   mapPanel?: React.ReactNode;
   /** Navigation bar — passed through to WizardLayout */
   navigation?: React.ReactNode;
+  /** Progress stepper */
+  progressStepper?: React.ReactNode;
+  /** Running total widget (e.g. CartButton) */
+  runningTotal?: React.ReactNode;
   /** MUI sx prop for the root */
   sx?: SxProps<Theme>;
 }
@@ -90,6 +94,8 @@ export const VenueStep: React.FC<VenueStepProps> = ({
   isPrePlanning = false,
   mapPanel,
   navigation,
+  progressStepper,
+  runningTotal,
   sx,
 }) => {
   const subheading = isPrePlanning
@@ -100,6 +106,8 @@ export const VenueStep: React.FC<VenueStepProps> = ({
     <WizardLayout
       variant="list-map"
       navigation={navigation}
+      progressStepper={progressStepper}
+      runningTotal={runningTotal}
       showBackLink
       backLabel="Back"
       onBack={onBack}