feat: update backend OCR parser, web app, mobile app camera/preview UI, tests, and documentation with sample images

lib/core/network/api_client.dart

@@ -50,7 +50,17 @@ class ApiClient {
         } else if (e.response != null) {
           // Standardized HTTP error formatting
           final statusCode = e.response?.statusCode;
-          errorMessage = 'Server error ($statusCode): ${e.response?.data['message'] ?? 'Unknown'}';
+          String serverMsg = 'Unknown';
+          final responseData = e.response?.data;
+          if (responseData is Map) {
+            serverMsg = responseData['message'] ?? 'Unknown';
+          } else if (responseData is String) {
+            // Truncate raw string if it's a long HTML page
+            serverMsg = responseData.length > 100 
+                ? '${responseData.substring(0, 100)}...' 
+                : responseData;
+          }
+          errorMessage = 'Server error ($statusCode): $serverMsg';
         } else if (e.type == DioExceptionType.connectionError) {
           errorMessage = 'No internet connection.';
         }