chore: replace flutter_markdown with flutter_markdown_plus (#147)

flutter_markdown 0.7.7+1 has been discontinued in favour of
flutter_markdown_plus. Switch the dependency and update both import
sites.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

lib/ui/screens/about_screen.dart

@@ -3,7 +3,7 @@ import 'dart:io';
 
 import 'package:flutter/material.dart';
 import 'package:flutter/services.dart';
-import 'package:flutter_markdown/flutter_markdown.dart';
+import 'package:flutter_markdown_plus/flutter_markdown_plus.dart';
 import 'package:flutter_riverpod/flutter_riverpod.dart';
 import 'package:package_info_plus/package_info_plus.dart';
 import 'package:sharedinbox/core/models/account.dart';

lib/ui/screens/changelog_screen.dart

@@ -2,7 +2,7 @@ import 'dart:async';
 
 import 'package:flutter/material.dart';
 import 'package:flutter/services.dart' show rootBundle;
-import 'package:flutter_markdown/flutter_markdown.dart';
+import 'package:flutter_markdown_plus/flutter_markdown_plus.dart';
 import 'package:url_launcher/url_launcher.dart';
 
 class ChangeLogScreen extends StatelessWidget {

pubspec.lock

@@ -379,14 +379,14 @@ packages:
       url: "https://pub.dev"
     source: hosted
     version: "8.0.0"
-  flutter_markdown:
+  flutter_markdown_plus:
     dependency: "direct main"
     description:
-      name: flutter_markdown
-      sha256: "08fb8315236099ff8e90cb87bb2b935e0a724a3af1623000a9cec930468e0f27"
+      name: flutter_markdown_plus
+      sha256: "039177906850278e8fb1cd364115ee0a46281135932fa8ecea8455522166d2de"
       url: "https://pub.dev"
     source: hosted
-    version: "0.7.7+1"
+    version: "1.0.7"
   flutter_plugin_android_lifecycle:
     dependency: transitive
     description:

pubspec.yaml

@@ -52,7 +52,7 @@ dependencies:
   # HTML rendering for email bodies
   webview_flutter: ^4.0.0
   url_launcher: ^6.3.2
-  flutter_markdown: ^0.7.7+1
+  flutter_markdown_plus: ^1.0.7
 
   # Background sync and local notifications
   flutter_local_notifications: ^18.0.1