Redesign menu admin screen with two-panel layout and modal forms

UX improvements:
- Two-panel layout: sticky category sidebar (desktop) + items grid
- Mobile: horizontal scrolling category pills above items
- Category sidebar shows item count badge per category; edit on hover
- Items search bar + instant filter (name, English name, Arabic name)
- Category filter drives items grid (click sidebar = filter items)
- Item cards: image hover reveals Edit button (progressive disclosure)
- Out-of-stock overlay + inline toggle switch (replaces text button)
- Add/Edit item opens in clean modal overlay (no jarring inline expansion)
- Add/Edit category opens in separate modal
- nameEn made optional (was blocking new item creation)
- Consolidated form state with single object per form
- Empty state with illustration and Add CTA
- Skeleton loading grid
- Branch overrides tab wired to branchId from store
- New i18n keys for search, counts, states in en/fa/ar

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

web/dashboard/messages/fa.json

@@ -668,7 +668,24 @@
     "media": "تصویر و ویدیو",
     "tabCatalog": "کاتالوگ",
     "tabBranch": "تنظیمات شعبه",
-    "selectBranchForOverrides": "برای تنظیم منوی شعبه، یک شعبه از بالا انتخاب کنید."
+    "selectBranchForOverrides": "برای تنظیم منوی شعبه، یک شعبه از بالا انتخاب کنید.",
+    "allItems": "همه آیتم‌ها",
+    "searchItemsPlaceholder": "جستجوی آیتم‌ها…",
+    "itemCount": "{count} آیتم",
+    "noItemsInCategory": "هنوز آیتمی در این دسته نیست",
+    "noItemsMatchSearch": "آیتمی با این عبارت یافت نشد",
+    "outOfStock": "ناموجود",
+    "newItem": "آیتم جدید",
+    "newCategory": "دسته جدید",
+    "editCategoryTitle": "ویرایش دسته",
+    "close": "بستن",
+    "saving": "در حال ذخیره…",
+    "model3d": "مدل سه‌بعدی",
+    "nameEnOptional": "نام انگلیسی (اختیاری)",
+    "addItemSuccess": "آیتم اضافه شد",
+    "updateItemSuccess": "آیتم به‌روز شد",
+    "addCategorySuccess": "دسته اضافه شد",
+    "updateCategorySuccess": "دسته به‌روز شد"
   },
   "branchMenu": {
     "title": "منوی شعبه",