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/pages/VenueStep/VenueStep.tsx

@@ -193,17 +193,6 @@ export const VenueStep: React.FC<VenueStepProps> = ({
         )
       }
     >
-      {/* Page heading */}
-      <Typography variant="display3" component="h1" sx={{ mb: 0.5 }} tabIndex={-1}>
-        Where would you like the service?
-      </Typography>
-
-      <Typography variant="body2" color="text.secondary" sx={{ mb: 3 }}>
-        {isPrePlanning
-          ? 'Browse available venues. Your choice can be changed later.'
-          : 'Choose a venue for the funeral service. You can filter by location, features, and religion.'}
-      </Typography>
-
       <Box
         component="form"
         noValidate
@@ -213,40 +202,63 @@ export const VenueStep: React.FC<VenueStepProps> = ({
           if (!loading) onContinue();
         }}
       >
-        {/* ─── Search + Filters ─── */}
-        <Box sx={{ mb: 3 }}>
-          <TextField
-            placeholder="Search a town or suburb..."
-            value={values.search}
-            onChange={(e) => onChange({ ...values, search: e.target.value })}
-            fullWidth
-            InputProps={{
-              startAdornment: (
-                <InputAdornment position="start">
-                  <SearchIcon sx={{ color: 'text.secondary' }} />
-                </InputAdornment>
-              ),
-            }}
-            sx={{ mb: 2 }}
-          />
+        {/* Sticky header — stays pinned while card list scrolls */}
+        <Box
+          sx={{
+            position: 'sticky',
+            top: 0,
+            zIndex: 1,
+            bgcolor: 'background.default',
+            pb: 1,
+            mx: -3,
+            px: 3,
+          }}
+        >
+          <Typography variant="display3" component="h1" sx={{ mb: 0.5 }} tabIndex={-1}>
+            Where would you like the service?
+          </Typography>
 
-          <Box sx={{ display: 'flex', gap: 1, flexWrap: 'wrap' }}>
-            {filterOptions.map((filter) => (
-              <Chip
-                key={filter.key}
-                label={filter.label}
-                onClick={() => handleFilterToggle(filter.key)}
-                selected={values.activeFilters.includes(filter.key)}
-              />
-            ))}
+          <Typography variant="body2" color="text.secondary" sx={{ mb: 3 }}>
+            {isPrePlanning
+              ? 'Browse available venues. Your choice can be changed later.'
+              : 'Choose a venue for the funeral service. You can filter by location, features, and religion.'}
+          </Typography>
+
+          {/* ─── Search + Filters ─── */}
+          <Box sx={{ mb: 2 }}>
+            <TextField
+              placeholder="Search a town or suburb..."
+              value={values.search}
+              onChange={(e) => onChange({ ...values, search: e.target.value })}
+              fullWidth
+              InputProps={{
+                startAdornment: (
+                  <InputAdornment position="start">
+                    <SearchIcon sx={{ color: 'text.secondary' }} />
+                  </InputAdornment>
+                ),
+              }}
+              sx={{ mb: 2 }}
+            />
+
+            <Box sx={{ display: 'flex', gap: 1, flexWrap: 'wrap' }}>
+              {filterOptions.map((filter) => (
+                <Chip
+                  key={filter.key}
+                  label={filter.label}
+                  onClick={() => handleFilterToggle(filter.key)}
+                  selected={values.activeFilters.includes(filter.key)}
+                />
+              ))}
+            </Box>
           </Box>
-        </Box>
 
-        {/* ─── Results count ─── */}
-        <Typography variant="body2" color="text.secondary" sx={{ mb: 2 }} aria-live="polite">
-          Found {venues.length} venue{venues.length !== 1 ? 's' : ''}
-          {locationName ? ` near ${locationName}` : ''}
-        </Typography>
+          {/* ─── Results count ─── */}
+          <Typography variant="body2" color="text.secondary" sx={{ mb: 0 }} aria-live="polite">
+            Found {venues.length} venue{venues.length !== 1 ? 's' : ''}
+            {locationName ? ` near ${locationName}` : ''}
+          </Typography>
+        </Box>
 
         {/* ─── Venue card grid ─── */}
         <Box