feat: add build mode, Dart version, timestamp to crash report (#205)

Show app version, build mode, and platform OS in the crash screen UI
so users can report bugs without needing to copy first.  The clipboard
report now also includes Build Mode (debug/release/profile), Dart
runtime version, and a UTC timestamp to aid post-crash diagnosis.

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

lib/ui/screens/crash_screen.dart

@@ -1,5 +1,6 @@
 import 'dart:io';
 
+import 'package:flutter/foundation.dart';
 import 'package:flutter/material.dart';
 import 'package:flutter/services.dart';
 import 'package:package_info_plus/package_info_plus.dart';
@@ -17,20 +18,35 @@ class CrashScreen extends StatelessWidget {
   final StackTrace? stackTrace;
   final String gitHash;
 
-  Future<String> _buildReport() async {
-    String version = 'unknown';
+  String get _buildMode {
+    if (kDebugMode) return 'debug';
+    if (kProfileMode) return 'profile';
+    return 'release';
+  }
+
+  Future<String> _fetchVersion() async {
     try {
       final info = await PackageInfo.fromPlatform();
-      version = '${info.version}+${info.buildNumber}';
-    } catch (_) {}
+      return '${info.version}+${info.buildNumber}';
+    } catch (_) {
+      return 'unknown';
+    }
+  }
+
+  Future<String> _buildReport() async {
+    final version = await _fetchVersion();
     final platform =
         '${Platform.operatingSystem} ${Platform.operatingSystemVersion}';
     final gitLine = gitHash.isNotEmpty
         ? 'Git Commit: [$gitHash](https://codeberg.org/guettli/sharedinbox/commit/$gitHash)\n'
         : '';
+    final timestamp = DateTime.now().toUtc().toIso8601String();
     return 'App Version: $version\n'
+        'Build Mode: $_buildMode\n'
         '$gitLine'
-        'Platform: $platform\n\n'
+        'Platform: $platform\n'
+        'Dart: ${Platform.version}\n'
+        'Timestamp: $timestamp\n\n'
         'Error:\n```\n$exception\n```\n\n'
         'Stack Trace:\n```\n$stackTrace\n```';
   }
@@ -56,6 +72,18 @@ class CrashScreen extends StatelessWidget {
                   style: Theme.of(ctx).textTheme.titleMedium,
                   textAlign: TextAlign.center,
                 ),
+                const SizedBox(height: 4),
+                FutureBuilder<String>(
+                  future: _fetchVersion(),
+                  builder: (context, snapshot) => Text(
+                    'v${snapshot.data ?? '…'}  •  $_buildMode  •  '
+                    '${Platform.operatingSystem} ${Platform.operatingSystemVersion}',
+                    style: Theme.of(context).textTheme.bodySmall?.copyWith(
+                          color: Colors.grey[600],
+                        ),
+                    textAlign: TextAlign.center,
+                  ),
+                ),
                 if (gitHash.isNotEmpty) ...[
                   const SizedBox(height: 8),
                   GestureDetector(

test/widget/crash_screen_test.dart

@@ -116,7 +116,10 @@ void main() {
 
       expect(clipboardText, isNotNull);
       expect(clipboardText, contains('App Version: 1.0.0+42'));
+      expect(clipboardText, contains('Build Mode:'));
       expect(clipboardText, contains('Platform:'));
+      expect(clipboardText, contains('Dart:'));
+      expect(clipboardText, contains('Timestamp:'));
       expect(clipboardText, contains('TestException: clipboard test'));
       // GIT_HASH is empty in test builds — no Git Commit line expected
       expect(clipboardText, isNot(contains('Git Commit:')));
@@ -167,6 +170,35 @@ void main() {
     },
   );
 
+  testWidgets(
+    'CrashScreen shows version, build mode, and platform in the UI',
+    (tester) async {
+      tester.view.physicalSize = const Size(800, 1200);
+      tester.view.devicePixelRatio = 1.0;
+      addTearDown(() => tester.view.resetPhysicalSize());
+
+      const exception = 'TestException: info row test';
+      final stackTrace = StackTrace.current;
+
+      await tester.pumpWidget(
+        MaterialApp(
+          home: CrashScreen(exception: exception, stackTrace: stackTrace),
+        ),
+      );
+      await tester.pumpAndSettle();
+
+      // Info row shows app version (from mock), build mode, and platform OS.
+      expect(find.textContaining('1.0.0+42'), findsWidgets);
+      // In test builds kDebugMode is true.
+      expect(find.textContaining('debug'), findsOneWidget);
+      // Platform OS is always present (linux in CI, android/ios on device).
+      expect(
+        find.textContaining(RegExp(r'linux|android|ios|windows|macos')),
+        findsWidgets,
+      );
+    },
+  );
+
   testWidgets(
     'CrashScreen used as root widget — buttons work without ScaffoldMessenger crash',
     (tester) async {