Add optional KYC flow and service-backed account limits

frontend/packages/sxchnge_kyc/lib/src/models/identity.dart

@@ -0,0 +1,54 @@
+import 'dart:typed_data';
+
+enum IdentityStatus { unverified, pending, approved, changesRequested, denied }
+
+enum ReviewReason {
+  passportUnreadable,
+  selfieUnreadable,
+  passportExpired,
+  unableToVerify,
+}
+
+enum PhotoKind { passport, selfie }
+
+enum KycError {
+  unavailable,
+  internal,
+  permission,
+  format,
+  tooLarge,
+  unreadable,
+  tooSmall,
+  incomplete,
+  sessionExpired,
+  rateLimited,
+  conflict,
+}
+
+class KycException implements Exception {
+  const KycException(this.code);
+  final KycError code;
+}
+
+class Identity {
+  const Identity({
+    required this.status,
+    this.reason,
+    this.submissionId,
+    this.simulated = false,
+  });
+  final IdentityStatus status;
+  final ReviewReason? reason;
+  final String? submissionId;
+  final bool simulated;
+  bool get canSubmit =>
+      status == IdentityStatus.unverified ||
+      status == IdentityStatus.changesRequested;
+}
+
+/// Ephemeral image data only. Never serialize this model into storage or telemetry.
+class Photo {
+  Photo(Uint8List bytes)
+    : bytes = Uint8List.fromList(bytes).asUnmodifiableView();
+  final Uint8List bytes;
+}