feat: implement BackButton component for consistent navigation

- Added BackButton component to standardize back navigation across pages.
- Integrated BackButton into various pages, replacing custom back buttons for consistency.
- Updated PageHeader to accept backTo prop for displaying BackButton when navigating from subpages.
- Created useGoBack hook to handle navigation logic, determining whether to go back in history or redirect to a fallback page.
- Added tests for BackButton and its integration with PageHeader to ensure expected behavior.

assets/admin/pages/AppointmentEditPage.tsx

@@ -11,6 +11,7 @@ import SearchableSelect from '../components/ui/SearchableSelect';
 import { WalletChargeLink } from '../components/AppointmentActions';
 import { formatRial, rialToToman, tomanToRial } from '../lib/utils';
 import { DEFAULT_SERVICE_CATEGORY } from '../lib/insuranceShares';
+import BackButton from '../components/ui/BackButton';
 import { useAppointmentInsurance } from '../hooks/useAppointmentInsurance';
 
 interface Option { uuid: string; name?: string; full_name?: string }
@@ -140,9 +141,7 @@ export default function AppointmentEditPage() {
   return (
     <div className="fade-in" style={{ maxWidth: 860, margin: '0 auto' }}>
       <div style={{ display: 'flex', justifyContent: 'flex-end', marginBottom: 14 }}>
-        <Link to={`/admin/appointments?date=${date}`} className="btn sm ghost" style={{ color: 'var(--text-2)' }}>
-          <ChevronRightIcon style={{ width: 16 }} /> بازگشت
-        </Link>
+        <BackButton fallback={`/admin/appointments?date=${date}`} />
       </div>
 
       <div style={{ background: 'var(--surface)', border: '1px solid var(--border)', borderRadius: 'var(--r-lg)', padding: 22 }}>