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/Dashboard.tsx

@@ -6,6 +6,7 @@ import {
   GripVertical, X
 } from 'lucide-react'
 import toast from 'react-hot-toast'
+import { showToast } from '../lib/toast'
 import {
   DragDropContext,
   Droppable,
@@ -93,7 +94,11 @@ function MealCard({ item, dragHandleProps, isDragging, onApprove: _onApprove, on
             {item.recipe?.servings} servings
           </p>
           <div className="flex items-center gap-1.5 mt-1">
-            <Badge variant={statusVariant} className="text-[10px] px-1.5 py-0.5">
+            <Badge
+              variant={statusVariant}
+              className="text-[10px] px-1.5 py-0.5"
+              aria-label={`Approval status: ${item.approval_status}`}
+            >
               {item.approval_status}
             </Badge>
             {item.estimated_cost && (
@@ -345,11 +350,28 @@ export default function Dashboard() {
   }
 
   async function handleDelete(itemId: string) {
-    if (!confirm('Delete this meal from the plan?')) return
+    if (!mealPlan) return
+    const item = mealPlan.items.find(i => i.id === itemId)
+    if (!item) return
     try {
       await mealPlannerApi.meals.deleteItem(itemId)
-      toast.success('Meal deleted')
       queryClient.invalidateQueries({ queryKey: ['mealPlan'] })
+      showToast.undo(
+        'Meal deleted',
+        async () => {
+          try {
+            await mealPlannerApi.meals.generateItem(
+              mealPlan.id,
+              item.day_of_week,
+              item.meal_type
+            )
+            queryClient.invalidateQueries({ queryKey: ['mealPlan'] })
+            toast.success('Slot filled with a new meal')
+          } catch (err: any) {
+            toast.error(err?.response?.data?.detail || 'Failed to refill slot')
+          }
+        }
+      )
     } catch (err: any) {
       toast.error(err?.response?.data?.detail || 'Failed to delete meal')
     }