feat: port inventory (انبارداری) page from tauri to admin dashboard

Add a per-tenant (doctor/clinic) Inventory domain and admin page, ported
from clinic-pro-tauri /inventory (which was static/mock) into a real feature.

Backend (src/Inventory/):
- Entities InventoryItem, InventoryPackage, InventoryPackageItem, scoped via
  entity_type/entity_id like TenantTag. Item status is derived, package total
  and availability derived at read time.
- InventoryService (stats, package assembly, availability), thin
  InventoryController with CRUD for items and packages + categories endpoint.
- Migration + docs/api/inventory.md + functional tests (10 tests, 42 assertions).

Frontend (assets/admin/):
- InventoryPage with two tabs (کالاهای مصرفی / پکیج), stat cards, items table
  (desktop + mobile cards), packages accordion, add/edit item and package
  modals, search + category filter — pixel-matched to the tauri source.
- useInventory hook (TanStack Query), route + sidebar link for doctor/clinic.
- Vitest coverage (real data, empty state, modal, packages tab).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

assets/admin/components/layout/Sidebar.tsx

@@ -1,4 +1,5 @@
 import {
+    ArchiveBoxIcon,
     ArrowLeftOnRectangleIcon,
     ArrowsRightLeftIcon,
     BanknotesIcon,
@@ -222,6 +223,11 @@ function buildSections(
                         label: "مطالبات بیمه",
                         feature: "insurance",
                     },
+                    {
+                        to: "/admin/inventory",
+                        icon: ArchiveBoxIcon,
+                        label: "انبارداری",
+                    },
                 ],
             },
             {
@@ -286,6 +292,11 @@ function buildSections(
                         label: "مطالبات بیمه",
                         feature: "insurance",
                     },
+                    {
+                        to: "/admin/inventory",
+                        icon: ArchiveBoxIcon,
+                        label: "انبارداری",
+                    },
                 ],
             },
             {