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/inventory/InventoryStatCards.tsx

@@ -0,0 +1,26 @@
+import React from 'react';
+import { ArchiveBoxIcon } from '@heroicons/react/24/outline';
+import StatCard from '../ui/StatCard';
+import { formatNumber } from '../../lib/utils';
+import type { InventoryStats } from '../../hooks/useInventory';
+
+const ICON = <ArchiveBoxIcon style={{ width: 20, height: 20 }} />;
+
+/** Four headline counters — order/colors mirror the tauri InventoryCards. */
+export default function InventoryStatCards({ stats }: { stats: InventoryStats }) {
+  return (
+    <div
+      style={{
+        display: 'grid',
+        gridTemplateColumns: 'repeat(auto-fit, minmax(220px, 1fr))',
+        gap: 20,
+        padding: '20px 0',
+      }}
+    >
+      <StatCard tone="violet" icon={ICON} label="تعداد کل کالاها"     value={formatNumber(stats.total)} />
+      <StatCard tone="amber"  icon={ICON} label="کالاهای کم موجود"    value={formatNumber(stats.low)} />
+      <StatCard tone="green"  icon={ICON} label="کالاهای موجود"       value={formatNumber(stats.inStock)} />
+      <StatCard tone="pink"   icon={ICON} label="کالاهای اتمام یافته" value={formatNumber(stats.outOfStock)} />
+    </div>
+  );
+}