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/pages/ProvidersStep/ProvidersStep.tsx

@@ -4,6 +4,7 @@ import type { SxProps, Theme } from '@mui/material/styles';
 import { WizardLayout } from '../../templates/WizardLayout';
 import { ProviderCard } from '../../molecules/ProviderCard';
 import { SearchBar } from '../../molecules/SearchBar';
+import { FilterPanel } from '../../molecules/FilterPanel';
 import { Chip } from '../../atoms/Chip';
 import { Typography } from '../../atoms/Typography';
 import { Button } from '../../atoms/Button';
@@ -62,6 +63,8 @@ export interface ProvidersStepProps {
   filters?: ProviderFilter[];
   /** Callback when a filter chip is toggled */
   onFilterToggle?: (index: number) => void;
+  /** Callback to clear all filters */
+  onFilterClear?: () => void;
   /** Callback for the Continue button */
   onContinue: () => void;
   /** Callback for the Back button */
@@ -105,6 +108,7 @@ export const ProvidersStep: React.FC<ProvidersStepProps> = ({
   onSearch,
   filters,
   onFilterToggle,
+  onFilterClear,
   onContinue,
   onBack,
   error,
@@ -165,32 +169,37 @@ export const ProvidersStep: React.FC<ProvidersStepProps> = ({
           {subheading}
         </Typography>
 
-        {/* Search bar */}
-        <Box sx={{ mb: 2 }}>
-          <SearchBar
-            value={searchQuery}
-            onChange={onSearchChange}
-            onSearch={onSearch}
-            placeholder="Search providers..."
-            size="small"
-          />
-        </Box>
-
-        {/* Filter chips */}
-        {filters && filters.length > 0 && (
-          <Box sx={{ display: 'flex', gap: 1, mb: 2, flexWrap: 'wrap' }}>
-            {filters.map((filter, index) => (
-              <Chip
-                key={filter.label}
-                label={filter.label}
-                selected={filter.active}
-                onClick={onFilterToggle ? () => onFilterToggle(index) : undefined}
-                variant="outlined"
-                size="small"
-              />
-            ))}
+        {/* Search bar + filter button */}
+        <Box sx={{ display: 'flex', gap: 1, mb: 2, alignItems: 'flex-start' }}>
+          <Box sx={{ flex: 1 }}>
+            <SearchBar
+              value={searchQuery}
+              onChange={onSearchChange}
+              onSearch={onSearch}
+              placeholder="Search providers..."
+              size="small"
+            />
           </Box>
-        )}
+          {filters && filters.length > 0 && (
+            <FilterPanel
+              activeCount={filters.filter((f) => f.active).length}
+              onClear={onFilterClear}
+            >
+              <Box sx={{ display: 'flex', flexDirection: 'column', gap: 1 }}>
+                {filters.map((filter, index) => (
+                  <Chip
+                    key={filter.label}
+                    label={filter.label}
+                    selected={filter.active}
+                    onClick={onFilterToggle ? () => onFilterToggle(index) : undefined}
+                    variant="outlined"
+                    size="small"
+                  />
+                ))}
+              </Box>
+            </FilterPanel>
+          )}
+        </Box>
 
         {/* Results count */}
         <Typography