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/DoctorFormPage.tsx

@@ -16,6 +16,7 @@ import SearchableSelect from '../components/ui/SearchableSelect';
 import MobileInput from '../components/ui/MobileInput';
 import PersianDatePicker from '../components/ui/PersianDatePicker';
 import { iranMobileSchema } from '../lib/utils';
+import BackButton from '../components/ui/BackButton';
 import { useAuthStore } from '../stores/authStore';
 
 // ── Types ────────────────────────────────────────────────────────────────────
@@ -307,6 +308,10 @@ export default function DoctorFormPage() {
   return (
     <div style={{ maxWidth: 680, margin: '0 auto' }} className="animate-slide-up">
 
+      <div style={{ marginBottom: 14 }}>
+        <BackButton fallback="/admin/doctors" />
+      </div>
+
       {/* Breadcrumb */}
       <div style={{ display: 'flex', alignItems: 'center', gap: 6, fontSize: 13, color: 'var(--text-3)', marginBottom: 20 }}>
         <button onClick={() => navigate('/admin/doctors')} style={{ display: 'flex', alignItems: 'center', gap: 4, background: 'none', border: 'none', cursor: 'pointer', color: 'var(--text-3)', fontSize: 13, padding: 0 }}>