Batch 2: List-map layout rework — 420px fixed column, sticky headers

- WizardLayout ListMapLayout: 420px fixed left column (D-B), flex:1
  right panel, back link rendered inside left panel instead of above
  the split (eliminates gap above map)
- LAYOUT_MAP type updated to accept backLink prop for list-map variant
- ProvidersStep: heading + search + filters wrapped in sticky Box
  that pins at top of scrollable left panel while card list scrolls
- VenueStep: same sticky header treatment, heading moved inside form
  for consistent wrapper structure

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

src/components/templates/WizardLayout/WizardLayout.tsx

@@ -142,11 +142,12 @@ const CenteredFormLayout: React.FC<{ children: React.ReactNode }> = ({ children
   </Container>
 );
 
-/** List + Map: ~40% scrollable list (left) / ~60% map (right) */
+/** List + Map: 420px fixed scrollable list (left) / flex map (right) — D-B */
 const ListMapLayout: React.FC<{
   children: React.ReactNode;
   secondaryPanel?: React.ReactNode;
-}> = ({ children, secondaryPanel }) => (
+  backLink?: React.ReactNode;
+}> = ({ children, secondaryPanel, backLink }) => (
   <Box
     sx={{
       display: 'flex',
@@ -156,18 +157,20 @@ const ListMapLayout: React.FC<{
   >
     <Box
       sx={{
-        width: { xs: '100%', md: '40%' },
+        width: { xs: '100%', md: 420 },
+        flexShrink: 0,
         overflowY: 'auto',
         px: { xs: 2, md: 3 },
         py: 3,
       }}
     >
+      {backLink}
       {children}
     </Box>
     <Box
       sx={{
-        display: { xs: 'none', md: 'block' },
-        width: '60%',
+        display: { xs: 'none', md: 'flex' },
+        flex: 1,
         position: 'relative',
       }}
     >
@@ -246,7 +249,11 @@ const DetailTogglesLayout: React.FC<{
 
 const LAYOUT_MAP: Record<
   WizardLayoutVariant,
-  React.FC<{ children: React.ReactNode; secondaryPanel?: React.ReactNode }>
+  React.FC<{
+    children: React.ReactNode;
+    secondaryPanel?: React.ReactNode;
+    backLink?: React.ReactNode;
+  }>
 > = {
   'centered-form': CenteredFormLayout,
   'list-map': ListMapLayout,
@@ -313,8 +320,8 @@ export const WizardLayout = React.forwardRef<HTMLDivElement, WizardLayoutProps>(
         {/* Stepper + running total bar (grid-sidebar, detail-toggles only) */}
         {showStepper && <StepperBar stepper={progressStepper} total={runningTotal} />}
 
-        {/* Back link — inside a container for consistent alignment */}
-        {showBackLink && (
+        {/* Back link — inside left panel for list-map, above content for others */}
+        {showBackLink && variant !== 'list-map' && (
           <Container
             maxWidth={variant === 'centered-form' ? 'sm' : 'lg'}
             sx={{ pt: 2, px: { xs: 4, md: 3 } }}
@@ -325,7 +332,16 @@ export const WizardLayout = React.forwardRef<HTMLDivElement, WizardLayoutProps>(
 
         {/* Main content area */}
         <Box component="main" sx={{ display: 'flex', flexDirection: 'column', flex: 1 }}>
-          <LayoutComponent secondaryPanel={secondaryPanel}>{children}</LayoutComponent>
+          <LayoutComponent
+            secondaryPanel={secondaryPanel}
+            backLink={
+              showBackLink && variant === 'list-map' ? (
+                <BackLink label={backLabel} onClick={onBack} />
+              ) : undefined
+            }
+          >
+            {children}
+          </LayoutComponent>
         </Box>
 
         {/* Sticky help bar */}