Add optional KYC flow and service-backed account limits

frontend/app/lib/kyc/preview.dart

@@ -0,0 +1,44 @@
+import 'package:flutter/material.dart';
+
+import 'package:sxchnge_kyc/sxchnge_kyc.dart';
+
+import '../generated/i18n/app_localizations.dart';
+
+/// Evict this sensitive preview's decoded cache entry on replacement or exit.
+class PhotoPreview extends StatefulWidget {
+  const PhotoPreview({super.key, required this.photo, required this.label});
+  final Photo photo;
+  final String label;
+  @override
+  State<PhotoPreview> createState() => _PhotoPreviewState();
+}
+
+class _PhotoPreviewState extends State<PhotoPreview> {
+  late ImageProvider _image = _provider();
+  ImageProvider _provider() =>
+      ResizeImage.resizeIfNeeded(1000, null, MemoryImage(widget.photo.bytes));
+  @override
+  void didUpdateWidget(covariant PhotoPreview oldWidget) {
+    super.didUpdateWidget(oldWidget);
+    if (!identical(oldWidget.photo, widget.photo)) {
+      _image.evict();
+      _image = _provider();
+    }
+  }
+
+  @override
+  void dispose() {
+    _image.evict();
+    super.dispose();
+  }
+
+  @override
+  Widget build(BuildContext context) => Image(
+    image: _image,
+    height: 220,
+    fit: BoxFit.contain,
+    semanticLabel: widget.label,
+    errorBuilder: (_, _, _) =>
+        Text(AppLocalizations.of(context)!.kycErrorUnreadable),
+  );
+}