feat(app): add vworld geocoding and native ads placeholders

lib/core/services/geocoding_service.dart

@@ -1,6 +1,7 @@
 import 'dart:convert';
 
 import 'package:http/http.dart' as http;
+import 'package:lunchpick/core/constants/api_keys.dart';
 import 'package:lunchpick/core/utils/app_logger.dart';
 
 /// 주소를 위도/경도로 변환하는 간단한 지오코딩(Geocoding) 서비스
@@ -16,6 +17,13 @@ class GeocodingService {
   Future<({double latitude, double longitude})?> geocode(String address) async {
     if (address.trim().isEmpty) return null;
 
+    // 1차: VWorld 지오코딩 시도 (키가 존재할 때만)
+    final vworldResult = await _geocodeWithVworld(address);
+    if (vworldResult != null) {
+      return vworldResult;
+    }
+
+    // 2차: Nominatim (fallback)
     try {
       final uri = Uri.parse(
         '$_endpoint?format=json&limit=1&q=${Uri.encodeQueryComponent(address)}',
@@ -55,4 +63,62 @@ class GeocodingService {
   ({double latitude, double longitude}) defaultCoordinates() {
     return (latitude: _fallbackLatitude, longitude: _fallbackLongitude);
   }
+
+  Future<({double latitude, double longitude})?> _geocodeWithVworld(
+    String address,
+  ) async {
+    final apiKey = ApiKeys.vworldApiKey;
+    if (apiKey.isEmpty) {
+      return null;
+    }
+
+    try {
+      final uri = Uri.https('api.vworld.kr', '/req/address', {
+        'service': 'address',
+        'request': 'getcoord',
+        'format': 'json',
+        'type': 'road', // 도로명 주소 기준
+        'key': apiKey,
+        'address': address,
+      });
+
+      final response = await http.get(
+        uri,
+        headers: const {'User-Agent': 'lunchpick-geocoder/1.0'},
+      );
+
+      if (response.statusCode != 200) {
+        AppLogger.debug(
+          '[GeocodingService] VWorld 실패 status: ${response.statusCode}',
+        );
+        return null;
+      }
+
+      final Map<String, dynamic> json = jsonDecode(response.body);
+      final responseNode = json['response'] as Map<String, dynamic>?;
+      if (responseNode == null || responseNode['status'] != 'OK') {
+        AppLogger.debug('[GeocodingService] VWorld 응답 오류: ${response.body}');
+        return null;
+      }
+
+      // VWorld 포인트는 WGS84 lon/lat 순서(x=lon, y=lat)
+      final result = responseNode['result'] as Map<String, dynamic>?;
+      final point = result?['point'] as Map<String, dynamic>?;
+      final x = point?['x']?.toString();
+      final y = point?['y']?.toString();
+      final lon = x != null ? double.tryParse(x) : null;
+      final lat = y != null ? double.tryParse(y) : null;
+      if (lat == null || lon == null) {
+        AppLogger.debug(
+          '[GeocodingService] VWorld 좌표 파싱 실패: ${point.toString()}',
+        );
+        return null;
+      }
+
+      return (latitude: lat, longitude: lon);
+    } catch (e) {
+      AppLogger.debug('[GeocodingService] VWorld 예외: $e');
+      return null;
+    }
+  }
 }