fix：增加图片选择和拍照功能

lib/features/assets/presentation/holding_detail_page.dart

@@ -1,4 +1,6 @@
-import 'package:flutter/material.dart';
+import 'dart:io';
+
+import 'package:flutter/material.dart' hide AssetImage;
 import 'package:go_router/go_router.dart';
 import 'package:hooks_riverpod/hooks_riverpod.dart';
 import 'package:shadcn_ui/shadcn_ui.dart';
@@ -10,6 +12,7 @@ import '../../profile/application/price_color_theme.dart';
 import '../../profile/application/profile_settings_controller.dart';
 import '../application/asset_portfolio_controller.dart';
 import '../data/asset_models.dart';
+import 'asset_image_preview_page.dart';
 
 class HoldingDetailPage extends ConsumerWidget {
   const HoldingDetailPage({super.key, this.id});
@@ -240,6 +243,8 @@ class HoldingDetailPage extends ConsumerWidget {
                     ),
                   ),
                   const SizedBox(height: 12),
+                  _buildImageSection(context, ref, holding),
+                  const SizedBox(height: 12),
                   Row(
                     children: [
                       Expanded(
@@ -362,6 +367,135 @@ class HoldingDetailPage extends ConsumerWidget {
     ).showSnackBar(const SnackBar(content: Text('已标记卖出 / 转赠')));
     Navigator.of(context).pop();
   }
+
+  Widget _buildImageSection(
+    BuildContext context,
+    WidgetRef ref,
+    GoldAssetHolding holding,
+  ) {
+    final images = holding.images;
+    return PrototypeCard(
+      padding: const EdgeInsets.fromLTRB(16, 16, 16, 16),
+      child: Column(
+        crossAxisAlignment: CrossAxisAlignment.start,
+        children: [
+          const Text(
+            '凭证照片',
+            style: TextStyle(fontSize: 13, color: Color(0xFF8A8780)),
+          ),
+          const SizedBox(height: 12),
+          if (images.isEmpty)
+            const Text(
+              '暂无凭证照片，可在添加资产时上传发票、证书或实物照片。',
+              style: TextStyle(fontSize: 12, color: Color(0xFFB3AFA5)),
+            )
+          else
+            Wrap(
+              spacing: 8,
+              runSpacing: 8,
+              children: [
+                for (var index = 0; index < images.length; index++)
+                  _buildDetailImageTile(
+                    context,
+                    ref,
+                    holding,
+                    images[index],
+                    index,
+                  ),
+              ],
+            ),
+        ],
+      ),
+    );
+  }
+
+  Widget _buildDetailImageTile(
+    BuildContext context,
+    WidgetRef ref,
+    GoldAssetHolding holding,
+    AssetImage image,
+    int index,
+  ) {
+    return GestureDetector(
+      onTap: () => _openImagePreview(context, holding.images, index),
+      onLongPress: () => _confirmDeleteImage(context, ref, holding, image),
+      child: ClipRRect(
+        borderRadius: BorderRadius.circular(12),
+        child: Stack(
+          children: [
+            Image.file(
+              File(image.localPath),
+              width: 84,
+              height: 84,
+              fit: BoxFit.cover,
+            ),
+            Positioned(
+              right: 4,
+              top: 4,
+              child: Container(
+                width: 20,
+                height: 20,
+                decoration: const BoxDecoration(
+                  color: Color(0xAA000000),
+                  shape: BoxShape.circle,
+                ),
+                child: const Icon(Icons.remove, size: 14, color: Colors.white),
+              ),
+            ),
+          ],
+        ),
+      ),
+    );
+  }
+
+  void _openImagePreview(
+    BuildContext context,
+    List<AssetImage> images,
+    int initialIndex,
+  ) {
+    Navigator.of(context).push(
+      MaterialPageRoute<void>(
+        builder: (_) => AssetImagePreviewPage(
+          images: images,
+          initialIndex: initialIndex,
+        ),
+      ),
+    );
+  }
+
+  void _confirmDeleteImage(
+    BuildContext context,
+    WidgetRef ref,
+    GoldAssetHolding holding,
+    AssetImage image,
+  ) {
+    showDialog<void>(
+      context: context,
+      builder: (ctx) => AlertDialog(
+        title: const Text('删除照片'),
+        content: const Text('确认删除这张凭证照片吗？'),
+        actions: [
+          TextButton(
+            onPressed: () => Navigator.of(ctx).pop(),
+            child: const Text('取消'),
+          ),
+          TextButton(
+            onPressed: () {
+              Navigator.of(ctx).pop();
+              final updated = holding.copyWith(
+                images: List<AssetImage>.unmodifiable(
+                  holding.images.where((item) => item.localId != image.localId).toList(),
+                ),
+                updatedAt: DateTime.now(),
+              );
+              ref.read(assetPortfolioControllerProvider.notifier).updateHolding(updated);
+            },
+            child: const Text('删除'),
+          ),
+        ],
+      ),
+    );
+  }
 }
 
 class _ActionMenuTile extends StatelessWidget {