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

lib/config/app_config.dart

@@ -1,12 +1,79 @@
+import 'dart:io';
 import 'package:flutter/material.dart';
 import 'package:google_fonts/google_fonts.dart';
 
 class AppConfig {
-  // API Configuration
-  static const String apiBaseUrl = 'http://192.168.80.84:3000/api/v1';
+  // ─── API Configuration ────────────────────────────────────────────────────
+  //
+  // Dual-Mode Configuration:
+  // - If public ngrok is running and active, the app will use it automatically.
+  // - If ngrok is down/inactive or unreachable, it falls back to the LAN/Local URL.
+  //
+
+  // LAN / WiFi / Emulator URL (port 8000 = nginx gateway)
+  // - Physical Device on same Wi-Fi: use 'http://192.168.70.7:8000/api/v1'
+  // - Android Emulator: use 'http://10.0.2.2:8000/api/v1'
+  // - iOS Simulator: use 'http://localhost:8000/api/v1'
+  static const String _lanBaseUrl = 'http://192.168.70.7:8000/api/v1';
+
+  // Ngrok public tunnel URL (update ini setiap ngrok di-restart)
+  static const String _ngrokBaseUrl = 'https://unlocated-waylon-potently.ngrok-free.dev/api/v1';
+
+  // Dynamic Base URL determined at startup
+  static String apiBaseUrl = _lanBaseUrl;
+
+  /// Dynamic URL resolver: Checks if the Ngrok tunnel is active.
+  /// If it returns a valid response (not 502/503/504), we use Ngrok.
+  /// Otherwise, we fall back to the LAN/Local base URL.
+  static Future<void> initializeApiBaseUrl() async {
+    final client = HttpClient();
+    client.connectionTimeout = const Duration(seconds: 2);
+    try {
+      debugPrint('AppConfig: Checking public Ngrok tunnel at $_ngrokBaseUrl/auth/login...');
+      final uri = Uri.parse('$_ngrokBaseUrl/auth/login');
+      final request = await client.postUrl(uri);
+      
+      // Add headers to bypass the ngrok browser warning page
+      request.headers.add('ngrok-skip-browser-warning', 'true');
+      request.headers.contentType = ContentType.json;
+      request.write('{}');
+      
+      final response = await request.close();
+      
+      final contentType = response.headers.contentType?.mimeType ?? '';
+      final ngrokErrorCode = response.headers.value('ngrok-error-code');
+
+      debugPrint('AppConfig: Ngrok response status: ${response.statusCode}, Content-Type: $contentType, Ngrok-Error-Code: $ngrokErrorCode');
+
+      // An active tunnel connected to our backend:
+      // 1. Should not return an ngrok-error-code header.
+      // 2. The response content-type should be JSON (our login API returns JSON).
+      // 3. Status code should not be 502, 503, or 504.
+      if (ngrokErrorCode == null && 
+          contentType.contains('json') && 
+          response.statusCode != 502 && 
+          response.statusCode != 503 && 
+          response.statusCode != 504) {
+        apiBaseUrl = _ngrokBaseUrl;
+        debugPrint('AppConfig: Ngrok tunnel is ACTIVE and backend responded. API Base URL: $apiBaseUrl');
+        return;
+      } else {
+        debugPrint('AppConfig: Ngrok is offline, inactive, or returned an error page.');
+      }
+    } catch (e) {
+      debugPrint('AppConfig: Ngrok connection failed or timed out: $e');
+    } finally {
+      client.close();
+    }
+    
+    apiBaseUrl = _lanBaseUrl;
+    debugPrint('AppConfig: Using Local/LAN API Base URL: $apiBaseUrl');
+  }
+
   static const String loginEndpoint = '/auth/login';
   static const String uploadDocumentEndpoint = '/documents/upload';
   static const String fetchDocumentsEndpoint = '/documents';
+
   
   // App Constants
   static const String appName = 'Prima Mart Scanner';