Feedback iteration: DialogShell, page consistency, popup standardisation

- Add DialogShell atom — shared dialog container (header, scrollable body, footer)
- Refactor FilterPanel to use DialogShell (Popover → centered Dialog)
- Refactor ArrangementDialog to use DialogShell
- Remove PreviewStep + AuthGateStep pages (consolidated into ArrangementDialog, D-E)
- IntroStep: static subheading, top-left aligned toggle button content
- ProvidersStep: h4 heading "Find a funeral director", location search with pin icon,
  filter moved below search right-aligned, map fill fix, hover scrollbar
- VenueStep: same consistency fixes (h4 heading, filter layout, location icon, map fix)
- PackagesStep: grouped packages ("Matching your preferences" / "Other packages from
  [Provider]"), removed budget filter + Most Popular badge, clickable provider card,
  onArrange replaces onContinue, h4 heading
- WizardLayout: list-map left panel gets thin scrollbar visible on hover

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

src/components/templates/WizardLayout/WizardLayout.tsx

@@ -170,6 +170,7 @@ const ListMapLayout: React.FC<{
       overflow: 'hidden',
     }}
   >
+    {/* Left panel — scrollable list with scrollbar visible on hover */}
     <Box
       sx={{
         width: { xs: '100%', md: 420 },
@@ -177,16 +178,31 @@ const ListMapLayout: React.FC<{
         overflowY: 'auto',
         px: { xs: 2, md: 3 },
         py: 3,
+        // Thin scrollbar, hidden until hover
+        scrollbarWidth: 'thin',
+        scrollbarColor: 'transparent transparent',
+        '&:hover': {
+          scrollbarColor: 'rgba(0,0,0,0.25) transparent',
+        },
+        '&::-webkit-scrollbar': { width: 6 },
+        '&::-webkit-scrollbar-thumb': {
+          background: 'transparent',
+          borderRadius: 3,
+        },
+        '&:hover::-webkit-scrollbar-thumb': {
+          background: 'rgba(0,0,0,0.25)',
+        },
       }}
     >
       {backLink}
       {children}
     </Box>
+    {/* Right panel — map or placeholder, fills available space */}
     <Box
       sx={{
         display: { xs: 'none', md: 'flex' },
         flex: 1,
-        position: 'relative',
+        minHeight: 0,
       }}
     >
       {secondaryPanel}