feat(mobile-app): 非强制更新时下载完成后让用户选择是否安装

- 强制更新：下载完成后自动安装
- 非强制更新：下载完成后显示"稍后安装"和"立即安装"按钮
- 更新提示对话框中"稍后"改为"暂时不更新"

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

frontend/mobile-app/lib/core/updater/channels/self_hosted_updater.dart

@@ -1,3 +1,4 @@
+import 'dart:io';
 import 'package:flutter/material.dart';
 import 'package:flutter_screenutil/flutter_screenutil.dart';
 import '../version_checker.dart';
@@ -202,7 +203,7 @@ class SelfHostedUpdater {
               TextButton(
                 onPressed: () => Navigator.pop(context),
                 child: Text(
-                  '稍后',
+                  '暂时不更新',
                   style: TextStyle(
                     fontSize: 14.sp,
                     color: const Color(0xFF78716C),
@@ -240,6 +241,7 @@ class SelfHostedUpdater {
       builder: (context) => _DownloadProgressDialog(
         versionInfo: versionInfo,
         downloadManager: downloadManager,
+        forceUpdate: versionInfo.forceUpdate,
       ),
     );
   }
@@ -254,10 +256,12 @@ class SelfHostedUpdater {
 class _DownloadProgressDialog extends StatefulWidget {
   final VersionInfo versionInfo;
   final DownloadManager downloadManager;
+  final bool forceUpdate;
 
   const _DownloadProgressDialog({
     required this.versionInfo,
     required this.downloadManager,
+    required this.forceUpdate,
   });
 
   @override
@@ -270,6 +274,8 @@ class _DownloadProgressDialogState extends State<_DownloadProgressDialog> {
   String _statusText = '准备下载...';
   bool _isDownloading = true;
   bool _hasError = false;
+  bool _downloadCompleted = false;
+  File? _downloadedApkFile;
 
   @override
   void initState() {
@@ -282,6 +288,7 @@ class _DownloadProgressDialogState extends State<_DownloadProgressDialog> {
       _statusText = '正在下载...';
       _isDownloading = true;
       _hasError = false;
+      _downloadCompleted = false;
     });
 
     final apkFile = await widget.downloadManager.downloadApk(
@@ -312,13 +319,34 @@ class _DownloadProgressDialogState extends State<_DownloadProgressDialog> {
       return;
     }
 
+    _downloadedApkFile = apkFile;
+
+    // 强制更新：直接安装
+    // 非强制更新：显示完成状态，让用户选择
+    if (widget.forceUpdate) {
+      setState(() {
+        _statusText = '下载完成，准备安装...';
+      });
+      await Future.delayed(const Duration(milliseconds: 500));
+      await _installApk();
+    } else {
+      setState(() {
+        _statusText = '下载完成';
+        _isDownloading = false;
+        _downloadCompleted = true;
+      });
+    }
+  }
+
+  Future<void> _installApk() async {
+    if (_downloadedApkFile == null) return;
+
     setState(() {
-      _statusText = '下载完成，准备安装...';
+      _statusText = '正在安装...';
+      _isDownloading = true;
     });
 
-    await Future.delayed(const Duration(milliseconds: 500));
-
-    final installed = await ApkInstaller.installApk(apkFile);
+    final installed = await ApkInstaller.installApk(_downloadedApkFile!);
 
     if (!mounted) return;
 
@@ -344,11 +372,20 @@ class _DownloadProgressDialogState extends State<_DownloadProgressDialog> {
 
   @override
   Widget build(BuildContext context) {
+    String title;
+    if (_downloadCompleted && !_hasError) {
+      title = '下载完成';
+    } else if (_hasError) {
+      title = '更新失败';
+    } else {
+      title = '正在更新';
+    }
+
     return PopScope(
-      canPop: !_isDownloading,
+      canPop: !_isDownloading && !widget.forceUpdate,
       child: AlertDialog(
         title: Text(
-          '正在更新',
+          title,
           style: TextStyle(
             fontSize: 18.sp,
             fontWeight: FontWeight.w600,
@@ -423,6 +460,30 @@ class _DownloadProgressDialogState extends State<_DownloadProgressDialog> {
               ),
             ),
           ],
+          // 非强制更新，下载完成后显示选择按钮
+          if (_downloadCompleted && !_hasError) ...[
+            TextButton(
+              onPressed: () => Navigator.pop(context),
+              child: Text(
+                '稍后安装',
+                style: TextStyle(
+                  fontSize: 14.sp,
+                  color: const Color(0xFF78716C),
+                ),
+              ),
+            ),
+            ElevatedButton(
+              onPressed: _installApk,
+              style: ElevatedButton.styleFrom(
+                backgroundColor: const Color(0xFFD4A84B),
+                foregroundColor: Colors.white,
+              ),
+              child: Text(
+                '立即安装',
+                style: TextStyle(fontSize: 14.sp),
+              ),
+            ),
+          ],
         ],
       ),
     );