feat: add app update checks and standalone release publishing panel

mobile/lib/app/hepan_app.dart

@@ -1,3 +1,5 @@
+import 'dart:async';
+
 import 'package:flutter/material.dart';
 import 'package:flutter_localizations/flutter_localizations.dart';
 
@@ -18,6 +20,8 @@ import '../features/school/school_selection_page.dart';
 import '../features/school/undergraduate/session.dart';
 import '../features/school/undergraduate/exam_query_picker.dart';
 import '../domain/undergraduate_exam_query.dart';
+import '../services/app_update_service.dart';
+import '../features/updates/update_prompt.dart';
 
 class HepanApp extends StatelessWidget {
   const HepanApp({
@@ -29,6 +33,8 @@ class HepanApp extends StatelessWidget {
     this.undergraduateBuilder,
     this.notificationSelection,
     this.feedbackSender,
+    this.updateService,
+    this.openUpdateDownload = openUpdateInBrowser,
   });
   final AppController controller;
   final Widget Function()? schoolBuilder;
@@ -37,6 +43,8 @@ class HepanApp extends StatelessWidget {
   final Widget Function()? undergraduateBuilder;
   final ValueNotifier<String?>? notificationSelection;
   final FeedbackSender? feedbackSender;
+  final AppUpdateService? updateService;
+  final UpdateDownloadOpener openUpdateDownload;
   @override
   Widget build(BuildContext context) => MaterialApp(
     debugShowCheckedModeBanner: false,
@@ -53,6 +61,8 @@ class HepanApp extends StatelessWidget {
       undergraduateBuilder: undergraduateBuilder,
       notificationSelection: notificationSelection,
       feedbackSender: feedbackSender ?? configuredFeedbackSender(),
+      updateService: updateService,
+      openUpdateDownload: openUpdateDownload,
     ),
   );
 }
@@ -66,6 +76,8 @@ class _Shell extends StatefulWidget {
     this.undergraduateBuilder,
     this.notificationSelection,
     required this.feedbackSender,
+    this.updateService,
+    required this.openUpdateDownload,
   });
   final AppController controller;
   final Widget Function()? schoolBuilder;
@@ -74,6 +86,8 @@ class _Shell extends StatefulWidget {
   final Widget Function()? undergraduateBuilder;
   final ValueNotifier<String?>? notificationSelection;
   final FeedbackSender feedbackSender;
+  final AppUpdateService? updateService;
+  final UpdateDownloadOpener openUpdateDownload;
   @override
   State<_Shell> createState() => _ShellState();
 }
@@ -81,6 +95,40 @@ class _Shell extends StatefulWidget {
 class _ShellState extends State<_Shell> with WidgetsBindingObserver {
   int _tab = 0;
   bool _openingSchool = false;
+  bool _checkingUpdate = false;
+  bool _updatePromptOpen = false;
+  Timer? _startupUpdate;
+  Future<void> _checkUpdate({bool silent = false}) async {
+    if (_checkingUpdate || _updatePromptOpen || widget.updateService == null) {
+      return;
+    }
+    setState(() => _checkingUpdate = true);
+    try {
+      final release = await widget.updateService!.check();
+      if (mounted) setState(() => _checkingUpdate = false);
+      if (!mounted || ModalRoute.of(context)?.isCurrent != true) return;
+      if (release != null) {
+        _updatePromptOpen = true;
+        await showUpdatePrompt(
+          context,
+          release,
+          openDownload: widget.openUpdateDownload,
+        );
+      } else if (!silent) {
+        ScaffoldMessenger.of(context)
+            .showSnackBar(const SnackBar(content: Text('当前已是最新版本')));
+      }
+    } on UpdateCheckException catch (error) {
+      if (!silent && mounted) {
+        ScaffoldMessenger.of(context)
+            .showSnackBar(SnackBar(content: Text(error.message)));
+      }
+    } finally {
+      _updatePromptOpen = false;
+      if (mounted) setState(() => _checkingUpdate = false);
+    }
+  }
+
   // Restore the saved school; legacy graduate imports infer their source.
   SupportedSchool? get _knownSchool =>
       widget.controller.snapshot.selectedSchool ??
@@ -102,10 +150,19 @@ class _ShellState extends State<_Shell> with WidgetsBindingObserver {
     WidgetsBinding.instance.addObserver(this);
     widget.notificationSelection?.addListener(_selectNotification);
     WidgetsBinding.instance.addPostFrameCallback((_) => _selectNotification());
+    if (widget.updateService != null) {
+      WidgetsBinding.instance.addPostFrameCallback((_) {
+        if (!mounted) return;
+        _startupUpdate = Timer(const Duration(seconds: 2), () {
+          if (mounted) unawaited(_checkUpdate(silent: true));
+        });
+      });
+    }
   }
 
   @override
   void dispose() {
+    _startupUpdate?.cancel();
     WidgetsBinding.instance.removeObserver(this);
     widget.notificationSelection?.removeListener(_selectNotification);
     super.dispose();
@@ -400,6 +457,10 @@ class _ShellState extends State<_Shell> with WidgetsBindingObserver {
                           ProfilePage(
                             controller: widget.controller,
                             feedbackSender: widget.feedbackSender,
+                            onCheckUpdates: widget.updateService == null
+                                ? null
+                                : () => _checkUpdate(),
+                            checkingUpdates: _checkingUpdate,
                             onLogin: () => _school(selectSchool: true),
                             schoolName: _knownSchool?.label,
                             onUpdateTerm: () => _school(chooseTerm: true),