fix: open HTML email links in external browser (S4)

flutter_html 3.0 does not auto-launch links — without an onLinkTap
callback, all anchor taps are silently dropped. Wire up launchUrl with
LaunchMode.externalApplication in both EmailDetailScreen (_SafeHtml)
and ThreadDetailScreen so every link in an HTML email body opens in the
user's preferred browser rather than doing nothing.

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

lib/ui/screens/email_detail_screen.dart

@@ -18,6 +18,14 @@ import 'package:url_launcher/url_launcher.dart';
 
 final _dateFmt = DateFormat('EEE, MMM d yyyy, HH:mm');
 
+void _openLink(String? url, Map<String, String> attrs, dynamic _) {
+  if (url == null) return;
+  final uri = Uri.tryParse(url);
+  if (uri != null) {
+    unawaited(launchUrl(uri, mode: LaunchMode.externalApplication));
+  }
+}
+
 class EmailDetailScreen extends ConsumerStatefulWidget {
   const EmailDetailScreen({super.key, required this.emailId});
   final String emailId;
@@ -553,7 +561,11 @@ class _SafeHtmlState extends State<_SafeHtml> {
       (_) => ErrorWidget.builder = prev,
     );
 
-    return Html(data: widget.data, extensions: widget.extensions);
+    return Html(
+      data: widget.data,
+      extensions: widget.extensions,
+      onLinkTap: _openLink,
+    );
   }
 }
 

lib/ui/screens/thread_detail_screen.dart

@@ -10,6 +10,7 @@ import 'package:sharedinbox/core/models/email.dart';
 import 'package:sharedinbox/core/models/undo_action.dart';
 import 'package:sharedinbox/core/utils/html_utils.dart';
 import 'package:sharedinbox/di.dart';
+import 'package:url_launcher/url_launcher.dart';
 
 final _dateFmt = DateFormat('EEE, MMM d, HH:mm');
 
@@ -168,6 +169,18 @@ class _EmailMessageCardState extends ConsumerState<_EmailMessageCard> {
                       extensions: [
                         if (!_loadRemoteImages) _BlockRemoteImagesExtension(),
                       ],
+                      onLinkTap: (url, _, __) {
+                        if (url == null) return;
+                        final uri = Uri.tryParse(url);
+                        if (uri != null) {
+                          unawaited(
+                            launchUrl(
+                              uri,
+                              mode: LaunchMode.externalApplication,
+                            ),
+                          );
+                        }
+                      },
                     ),
                   ] else
                     SelectableText(