feat: add DigitInput component; force English digits for phone & national code

New reusable DigitInput normalizes Persian/Arabic digits to English on
input, strips non-digits, enforces maxDigits, and is always LTR + numeric
keyboard. Use it for the phone and national-code fields on the appointment
create page (phone previously kept raw Persian digits; national code lost
Persian digits to the \D strip).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

assets/admin/components/ui/DigitInput.test.tsx

@@ -0,0 +1,29 @@
+import { describe, it, expect, vi } from 'vitest';
+import { render, screen, fireEvent } from '@testing-library/react';
+import DigitInput from './DigitInput';
+
+describe('DigitInput — ورودی عددی با تبدیل رقم فارسی', () => {
+  it('converts Persian/Arabic digits to English (happy path)', () => {
+    const onChange = vi.fn();
+    render(<DigitInput value="" onChange={onChange} placeholder="p" />);
+    fireEvent.change(screen.getByPlaceholderText('p'), { target: { value: '۰۹۱۲٣٤' } });
+    expect(onChange).toHaveBeenCalledWith('091234');
+  });
+
+  it('strips non-digit characters (error/garbage input)', () => {
+    const onChange = vi.fn();
+    render(<DigitInput value="" onChange={onChange} placeholder="p" />);
+    fireEvent.change(screen.getByPlaceholderText('p'), { target: { value: '0a9 1-2b' } });
+    expect(onChange).toHaveBeenCalledWith('0912');
+  });
+
+  it('enforces maxDigits and handles empty input (boundary)', () => {
+    const onChange = vi.fn();
+    render(<DigitInput value="" onChange={onChange} maxDigits={10} placeholder="p" />);
+    const input = screen.getByPlaceholderText('p');
+    fireEvent.change(input, { target: { value: '۱۲۳۴۵۶۷۸۹۰۱۲' } });
+    expect(onChange).toHaveBeenCalledWith('1234567890');
+    expect(input).toHaveAttribute('dir', 'ltr');
+    expect(input).toHaveAttribute('inputmode', 'numeric');
+  });
+});