feat(ui): close 3 P2 audit findings + a11y sweep (Sprint 3)

- lib/toast.tsx (renamed from .ts for JSX): new showToast.undo(message,
  onUndo, ms=5000) helper. Inline 'Undo' button dismisses the toast and
  fires onUndo. Note: react-hot-toast 2.6 lacks onClose/onDismiss, so
  expiry is silent — same effective behavior as confirm() declined.

- Dashboard.handleDelete: captures the full MealPlanItem before the
  DELETE so Undo can re-fire meals.generateItem(planId, dayOfWeek,
  mealType) and refill the slot (recipe may differ — see plan R4).

- Pantry.handleRemove: fully reversible — Undo re-fires pantry.add with
  the original ingredient_id, quantity, and unit. New removeId state
  scopes the spinner to the clicked row.

- Both confirm() call sites removed.

- App.tsx Navigation: whitespace-nowrap + px-2 sm:px-3 so all 4 links fit
  on one line down to 360 px. aria-current='page' on the active link.
  <nav aria-label='Primary'>, <main id='main-content'>.

- components/ui/Badge: optional icon and aria-label props. Dashboard
  approval-status Badge passes aria-label='Approval status: approved'
  (or the current value) so screen readers don't rely on color alone.

- ErrorBoundary already mounted at App.tsx:42 — verified, no code change.

- Review/sprint3-verification.md (new) + Review/ui-nielsen-audit.md and
  fix-ui-audit.md updated with Sprint 3 status and deploy steps.

Build: npm run build (tsc + vite) green. tsc 0 errors.

frontend/src/pages/Pantry.tsx

@@ -19,6 +19,7 @@ const AISLE_OPTIONS = [
 export default function Pantry() {
   const queryClient = useQueryClient()
   const [showAddForm, setShowAddForm] = useState(false)
+  const [removeId, setRemoveId] = useState<string | null>(null)
   const [searchQuery, setSearchQuery] = useState('')
 
   /* ingredient name typed by user */
@@ -71,12 +72,46 @@ export default function Pantry() {
     onSuccess: () => {
       queryClient.invalidateQueries({ queryKey: ['pantry'] })
       showToast.success('Item removed')
+      setRemoveId(null)
     },
     onError: () => {
       showToast.error('Failed to remove item')
+      setRemoveId(null)
     },
   })
 
+  async function handleRemove(item: HomePantryItem) {
+    if (!item.ingredient_id) {
+      showToast.error('Cannot remove: missing ingredient link')
+      return
+    }
+    setRemoveId(item.id)
+    try {
+      await mealPlannerApi.pantry.remove(item.id)
+      queryClient.invalidateQueries({ queryKey: ['pantry'] })
+      showToast.undo(
+        'Item removed',
+        async () => {
+          try {
+            await mealPlannerApi.pantry.add({
+              ingredient_id: item.ingredient_id!,
+              quantity: item.quantity,
+              unit: item.unit,
+            })
+            queryClient.invalidateQueries({ queryKey: ['pantry'] })
+            showToast.success('Item restored')
+          } catch {
+            showToast.error('Failed to restore item')
+          }
+        }
+      )
+    } catch {
+      showToast.error('Failed to remove item')
+    } finally {
+      setRemoveId(null)
+    }
+  }
+
   async function handleAdd() {
     const name = ingredientName.trim()
     if (!name) {
@@ -313,12 +348,8 @@ export default function Pantry() {
                           variant="ghost"
                           size="sm"
                           icon={<Trash2 className="w-4 h-4" />}
-                          onClick={() => {
-                            if (confirm(`Remove ${item.ingredient?.name || 'this item'} from pantry?`)) {
-                              removeMutation.mutate(item.id)
-                            }
-                          }}
-                          loading={removeMutation.isPending}
+                          onClick={() => handleRemove(item)}
+                          loading={removeMutation.isPending && removeId === item.id}
                           disabled={removeMutation.isPending}
                         >
                           Remove