feat(discount): dedicated «مدیریت تخفیف‌ها» item in the settings menu

Add a standalone settings sidebar entry + route (/admin/discounts) rendering
DiscountsPage (DiscountTab inside SettingsLayout, doctor/clinic only), and
revert the temporary tab inside the subscription page. Cleaner, discoverable
placement.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

assets/admin/pages/DiscountsPage.tsx

@@ -0,0 +1,17 @@
+import SettingsLayout from '../components/layout/SettingsLayout';
+import DiscountTab from '../components/DiscountTab';
+
+/** مدیریت تخفیف‌ها — بخش تنظیمات برای تعریف قوانین تخفیف عمومی (owner-scoped). */
+export default function DiscountsPage() {
+  return (
+    <SettingsLayout active="discounts">
+      <div
+        style={{ background: 'var(--surface)', minWidth: 0 }}
+        className="px-4 py-4 md:px-6 md:py-6 rounded-[var(--r-lg)]"
+      >
+        <h1 className="section-title" style={{ marginBottom: 16 }}>مدیریت تخفیف‌ها</h1>
+        <DiscountTab />
+      </div>
+    </SettingsLayout>
+  );
+}