feat(policy-explorer-v2): implement Phase 4 - Enhanced Filtering

✨ New Features (Tasks T023-T028)
- PolicyTypeFilter component with multi-select checkboxes
- 8 common Intune policy types (deviceConfiguration, compliancePolicy, etc.)
- Active filter badges with individual remove buttons
- 'Clear All Filters' button when filters active
- Filter count badge in dropdown trigger

🔧 Updates
- PolicyTableToolbar now accepts filter props
- PolicyExplorerV2Client connects filters to URL state
- Filters sync with URL for shareable links
- Filter state triggers data refetch automatically

📦 Dependencies
- Added shadcn DropdownMenu component

✅ Zero TypeScript compilation errors
✅ All Phase 4 tasks complete (T023-T028)
✅ Ready for Phase 5 (CSV Export)

Refs: specs/004-policy-explorer-v2/tasks.md Phase 4

app/(app)/search/PolicyExplorerV2Client.tsx

@@ -147,6 +147,10 @@ export function PolicyExplorerV2Client() {
         table={table}
         density={preferences.density}
         onDensityChange={handleDensityChange}
+        selectedPolicyTypes={urlState.policyTypes}
+        onSelectedPolicyTypesChange={urlState.updatePolicyTypes}
+        searchQuery={urlState.searchQuery}
+        onSearchQueryChange={urlState.updateSearchQuery}
       />
 
       {/* Table */}

components/policy-explorer/PolicyTableToolbar.tsx

@@ -12,7 +12,9 @@
 
 import { Button } from '@/components/ui/button';
 import { ColumnVisibilityMenu } from './ColumnVisibilityMenu';
-import { LayoutList, LayoutGrid } from 'lucide-react';
+import { PolicyTypeFilter } from './PolicyTypeFilter';
+import { LayoutList, LayoutGrid, X } from 'lucide-react';
+import { Badge } from '@/components/ui/badge';
 import type { Table } from '@tanstack/react-table';
 import type { PolicySettingRow } from '@/lib/types/policy-table';
 
@@ -20,17 +22,79 @@ interface PolicyTableToolbarProps {
   table: Table<PolicySettingRow>;
   density: 'compact' | 'comfortable';
   onDensityChange: (density: 'compact' | 'comfortable') => void;
+  // Filter props
+  selectedPolicyTypes: string[];
+  onSelectedPolicyTypesChange: (types: string[]) => void;
+  searchQuery: string;
+  onSearchQueryChange: (query: string) => void;
 }
 
 export function PolicyTableToolbar({
   table,
   density,
   onDensityChange,
+  selectedPolicyTypes,
+  onSelectedPolicyTypesChange,
+  searchQuery,
+  onSearchQueryChange,
 }: PolicyTableToolbarProps) {
+  const hasActiveFilters = selectedPolicyTypes.length > 0 || searchQuery.length > 0;
+
+  const handleClearFilters = () => {
+    onSelectedPolicyTypesChange([]);
+    onSearchQueryChange('');
+  };
+
   return (
     <div className="flex items-center justify-between">
       <div className="flex flex-1 items-center space-x-2">
-        {/* Search and filters will be added here in Phase 4 */}
+        {/* Policy Type Filter */}
+        <PolicyTypeFilter
+          selectedTypes={selectedPolicyTypes}
+          onSelectedTypesChange={onSelectedPolicyTypesChange}
+        />
+
+        {/* Active Filter Badges */}
+        {selectedPolicyTypes.length > 0 && (
+          <div className="flex items-center gap-1">
+            {selectedPolicyTypes.slice(0, 2).map((type) => (
+              <Badge
+                key={type}
+                variant="secondary"
+                className="h-6 px-2 text-xs"
+              >
+                {type}
+                <button
+                  onClick={() =>
+                    onSelectedPolicyTypesChange(
+                      selectedPolicyTypes.filter((t) => t !== type)
+                    )
+                  }
+                  className="ml-1 hover:text-destructive"
+                >
+                  <X className="h-3 w-3" />
+                </button>
+              </Badge>
+            ))}
+            {selectedPolicyTypes.length > 2 && (
+              <Badge variant="secondary" className="h-6 px-2 text-xs">
+                +{selectedPolicyTypes.length - 2} more
+              </Badge>
+            )}
+          </div>
+        )}
+
+        {/* Clear All Filters Button */}
+        {hasActiveFilters && (
+          <Button
+            variant="ghost"
+            size="sm"
+            onClick={handleClearFilters}
+            className="h-8 px-2 lg:px-3"
+          >
+            Clear filters
+          </Button>
+        )}
       </div>
 
       <div className="flex items-center space-x-2">

components/policy-explorer/PolicyTypeFilter.tsx

@@ -0,0 +1,125 @@
+/**
+ * PolicyTypeFilter Component
+ * 
+ * Multi-select checkbox dropdown for filtering by policy types.
+ * 
+ * Features:
+ * - Checkbox list of all available policy types
+ * - "Select All" / "Clear All" actions
+ * - Active filter count badge
+ * - Syncs with URL state via useURLState hook
+ */
+
+'use client';
+
+import { useState } from 'react';
+import { Button } from '@/components/ui/button';
+import {
+  DropdownMenu,
+  DropdownMenuCheckboxItem,
+  DropdownMenuContent,
+  DropdownMenuLabel,
+  DropdownMenuSeparator,
+  DropdownMenuTrigger,
+} from '@/components/ui/dropdown-menu';
+import { Badge } from '@/components/ui/badge';
+import { Filter } from 'lucide-react';
+
+// Common Intune policy types
+const POLICY_TYPES = [
+  { value: 'deviceConfiguration', label: 'Device Configuration' },
+  { value: 'compliancePolicy', label: 'Compliance Policy' },
+  { value: 'deviceManagementScript', label: 'Device Management Script' },
+  { value: 'windowsUpdateForBusiness', label: 'Windows Update for Business' },
+  { value: 'iosUpdateConfiguration', label: 'iOS Update Configuration' },
+  { value: 'macOSExtensionsConfiguration', label: 'macOS Extensions' },
+  { value: 'settingsCatalog', label: 'Settings Catalog' },
+  { value: 'endpointProtection', label: 'Endpoint Protection' },
+] as const;
+
+interface PolicyTypeFilterProps {
+  selectedTypes: string[];
+  onSelectedTypesChange: (types: string[]) => void;
+}
+
+export function PolicyTypeFilter({
+  selectedTypes,
+  onSelectedTypesChange,
+}: PolicyTypeFilterProps) {
+  const [open, setOpen] = useState(false);
+
+  const handleSelectAll = () => {
+    onSelectedTypesChange(POLICY_TYPES.map(t => t.value));
+  };
+
+  const handleClearAll = () => {
+    onSelectedTypesChange([]);
+  };
+
+  const handleToggleType = (type: string) => {
+    if (selectedTypes.includes(type)) {
+      onSelectedTypesChange(selectedTypes.filter(t => t !== type));
+    } else {
+      onSelectedTypesChange([...selectedTypes, type]);
+    }
+  };
+
+  const activeCount = selectedTypes.length;
+  const allSelected = activeCount === POLICY_TYPES.length;
+  const noneSelected = activeCount === 0;
+
+  return (
+    <DropdownMenu open={open} onOpenChange={setOpen}>
+      <DropdownMenuTrigger asChild>
+        <Button variant="outline" size="sm" className="h-8">
+          <Filter className="mr-2 h-4 w-4" />
+          Policy Type
+          {activeCount > 0 && (
+            <Badge variant="secondary" className="ml-2 h-5 px-1.5">
+              {activeCount}
+            </Badge>
+          )}
+        </Button>
+      </DropdownMenuTrigger>
+      <DropdownMenuContent align="start" className="w-[250px]">
+        <DropdownMenuLabel>Filter by Policy Type</DropdownMenuLabel>
+        <DropdownMenuSeparator />
+        
+        {/* Quick Actions */}
+        <div className="flex items-center justify-between px-2 py-1.5">
+          <Button
+            variant="ghost"
+            size="sm"
+            onClick={handleSelectAll}
+            disabled={allSelected}
+            className="h-7 text-xs"
+          >
+            Select All
+          </Button>
+          <Button
+            variant="ghost"
+            size="sm"
+            onClick={handleClearAll}
+            disabled={noneSelected}
+            className="h-7 text-xs"
+          >
+            Clear All
+          </Button>
+        </div>
+        
+        <DropdownMenuSeparator />
+        
+        {/* Policy Type Checkboxes */}
+        {POLICY_TYPES.map((type) => (
+          <DropdownMenuCheckboxItem
+            key={type.value}
+            checked={selectedTypes.includes(type.value)}
+            onCheckedChange={() => handleToggleType(type.value)}
+          >
+            {type.label}
+          </DropdownMenuCheckboxItem>
+        ))}
+      </DropdownMenuContent>
+    </DropdownMenu>
+  );
+}