feat: Implement update checker and dialog for available app updates with localization support

lib/models/update_info.dart

@@ -0,0 +1,52 @@
+/// Information about an available app update
+class UpdateInfo {
+  final bool isAvailable;
+  final String currentCommitHash;
+  final String? latestCommitHash;
+  final String? downloadUrl;
+  final String? buildId;
+  final String? timestamp;
+
+  const UpdateInfo({
+    required this.isAvailable,
+    required this.currentCommitHash,
+    this.latestCommitHash,
+    this.downloadUrl,
+    this.buildId,
+    this.timestamp,
+  });
+
+  /// Factory constructor for when no update is available
+  factory UpdateInfo.noUpdate(String currentCommitHash) {
+    return UpdateInfo(
+      isAvailable: false,
+      currentCommitHash: currentCommitHash,
+    );
+  }
+
+  /// Factory constructor for when an update is available
+  factory UpdateInfo.available({
+    required String currentCommitHash,
+    required String latestCommitHash,
+    required String downloadUrl,
+    String? buildId,
+    String? timestamp,
+  }) {
+    return UpdateInfo(
+      isAvailable: true,
+      currentCommitHash: currentCommitHash,
+      latestCommitHash: latestCommitHash,
+      downloadUrl: downloadUrl,
+      buildId: buildId,
+      timestamp: timestamp,
+    );
+  }
+
+  @override
+  String toString() {
+    return 'UpdateInfo(isAvailable: $isAvailable, '
+        'current: $currentCommitHash, '
+        'latest: $latestCommitHash, '
+        'downloadUrl: $downloadUrl)';
+  }
+}