Replace phone verification with canvas signature on confirm page

Adds a canvas-based SignaturePad component used on the customer
confirm page. Authorize now requires a non-empty signature; reject
opens a required reason modal. The archived signature is shown to
the customer after confirming and on the admin detail page.

Also fixes the confirm page being clipped at the top when its
content exceeds the viewport: the public layout used
height:100vh + overflow:hidden which cropped the centered card.
Switched to min-height:100vh so tall content can scroll naturally.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

src/pages/AftersalesDetail.tsx

@@ -322,6 +322,30 @@ function AftersalesDetailPage() {
           </Descriptions.Item>
         </Descriptions>
 
+        {order.authorizationStatus === 'authorized' && order.signature && (
+          <div style={{ marginBottom: 24 }}>
+            <div style={{ fontSize: 13, color: '#595959', marginBottom: 8 }}>
+              客户签名
+              {order.confirmedAt && (
+                <span style={{ marginLeft: 12, color: '#8c8c8c', fontSize: 12 }}>
+                  签署时间：{new Date(order.confirmedAt).toLocaleString('zh-CN')}
+                </span>
+              )}
+            </div>
+            <img
+              src={order.signature}
+              alt="客户签名"
+              style={{
+                maxWidth: 480,
+                width: '100%',
+                border: '1px solid #f0f0f0',
+                borderRadius: 6,
+                background: '#fff',
+              }}
+            />
+          </div>
+        )}
+
         <Form form={form} layout="vertical" onFinish={handleSave} disabled={!canEdit}>
           <Form.Item
             name="companyAddress"