Batch 3: FilterPanel molecule + integration across 3 steps (D-C, D-F)

New molecule:
- FilterPanel: Popover-based reusable filter trigger with active
  count badge, Clear all, Done actions. D-C: Popover for MVP.

Step integrations:
- ProvidersStep: inline Chip filter bar → FilterPanel Popover,
  search bar + filter button side-by-side in sticky header
- VenueStep: same pattern, filter chips moved into Popover
- CoffinsStep (D-F): grid-sidebar layout → wide-form (full-width
  4-col grid), category + price selects moved into FilterPanel

WizardLayout:
- Added wide-form variant (maxWidth lg, single column) for
  card grids that benefit from full width
- wide-form included in STEPPER_VARIANTS for progress bar

Storybook:
- FilterPanel stories: Default, WithActiveFilters, SelectFilters,
  CustomLabel

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

src/components/templates/WizardLayout/WizardLayout.tsx

@@ -9,9 +9,10 @@ import { Typography } from '../../atoms/Typography';
 
 // ─── Types ───────────────────────────────────────────────────────────────────
 
-/** Layout variant matching the 5 wizard page templates */
+/** Layout variant matching the wizard page templates */
 export type WizardLayoutVariant =
   | 'centered-form'
+  | 'wide-form'
   | 'list-map'
   | 'list-detail'
   | 'grid-sidebar'
@@ -142,6 +143,20 @@ const CenteredFormLayout: React.FC<{ children: React.ReactNode }> = ({ children
   </Container>
 );
 
+/** Wide Form: single column maxWidth "lg", for card grids (coffins, etc.) */
+const WideFormLayout: React.FC<{ children: React.ReactNode }> = ({ children }) => (
+  <Container
+    maxWidth="lg"
+    sx={{
+      py: { xs: 4, md: 6 },
+      px: { xs: 2, md: 3 },
+      flex: 1,
+    }}
+  >
+    {children}
+  </Container>
+);
+
 /** List + Map: 420px fixed scrollable list (left) / flex map (right) — D-B */
 const ListMapLayout: React.FC<{
   children: React.ReactNode;
@@ -256,6 +271,7 @@ const LAYOUT_MAP: Record<
   }>
 > = {
   'centered-form': CenteredFormLayout,
+  'wide-form': WideFormLayout,
   'list-map': ListMapLayout,
   'list-detail': ListDetailLayout,
   'grid-sidebar': GridSidebarLayout,
@@ -263,7 +279,7 @@ const LAYOUT_MAP: Record<
 };
 
 /** Variants that show the stepper/total bar */
-const STEPPER_VARIANTS: WizardLayoutVariant[] = ['grid-sidebar', 'detail-toggles'];
+const STEPPER_VARIANTS: WizardLayoutVariant[] = ['wide-form', 'grid-sidebar', 'detail-toggles'];
 
 // ─── Component ───────────────────────────────────────────────────────────────