feat: implement global error handling with reusable dialog and widget for improved user feedback

Co-authored-by: Copilot <copilot@github.com>

flutter/lib/core/utils/global_error_handler.dart

@@ -0,0 +1,38 @@
+import 'package:flutter/material.dart';
+import 'package:flutter/services.dart';
+
+/// Visar en global dialogruta med ett felmeddelande och en kopieringsknapp.
+void showGlobalErrorDialog(BuildContext context, String errorMessage) {
+  showDialog(
+    context: context,
+    builder: (BuildContext context) {
+      return AlertDialog(
+        title: const Text('Fel'),
+        content: Column(
+          mainAxisSize: MainAxisSize.min,
+          crossAxisAlignment: CrossAxisAlignment.start,
+          children: [
+            SelectableText(errorMessage),
+          ],
+        ),
+        actions: <Widget>[
+          TextButton(
+            child: const Text('Stäng'),
+            onPressed: () {
+              Navigator.of(context).pop();
+            },
+          ),
+          TextButton(
+            child: const Text('Kopiera'),
+            onPressed: () {
+              Clipboard.setData(ClipboardData(text: errorMessage));
+              ScaffoldMessenger.of(context).showSnackBar(
+                const SnackBar(content: Text('Felmeddelande kopierat!')),
+              );
+            },
+          ),
+        ],
+      );
+    },
+  );
+}

flutter/lib/core/widgets/error_message_widget.dart

@@ -0,0 +1,40 @@
+import 'package:flutter/material.dart';
+import 'package:flutter/services.dart';
+
+/// En återanvändbar widget för att visa felmeddelanden med en kopieringsknapp.
+class ErrorMessageWidget extends StatelessWidget {
+  final String errorMessage;
+
+  const ErrorMessageWidget({Key? key, required this.errorMessage}) : super(key: key);
+
+  @override
+  Widget build(BuildContext context) {
+    return AlertDialog(
+      title: const Text('Fel'),
+      content: Column(
+        mainAxisSize: MainAxisSize.min,
+        crossAxisAlignment: CrossAxisAlignment.start,
+        children: [
+          SelectableText(errorMessage),
+        ],
+      ),
+      actions: <Widget>[
+        TextButton(
+          child: const Text('Stäng'),
+          onPressed: () {
+            Navigator.of(context).pop();
+          },
+        ),
+        TextButton(
+          child: const Text('Kopiera'),
+          onPressed: () {
+            Clipboard.setData(ClipboardData(text: errorMessage));
+            ScaffoldMessenger.of(context).showSnackBar(
+              const SnackBar(content: Text('Felmeddelande kopierat!')),
+            );
+          },
+        ),
+      ],
+    );
+  }
+}