feat: Implement S3 image handling with a new resolver and widget, update agent display, and configure storage base URL.

lib/core/utils/image_url_resolver.dart

@@ -0,0 +1,63 @@
+import 'package:dio/dio.dart';
+import 'package:real_estate_mobile/core/network/api_client.dart';
+
+/// Resolves S3 keys to presigned download URLs via the backend API.
+/// Caches results in memory to avoid repeated API calls.
+class ImageUrlResolver {
+  ImageUrlResolver._();
+  static final ImageUrlResolver instance = ImageUrlResolver._();
+
+  final Map<String, String> _cache = {};
+  final Map<String, Future<String?>> _pending = {};
+
+  /// Returns a direct image URL.
+  /// - If [imageUrl] is already an http(s) URL, returns it as-is.
+  /// - If it's an S3 key, fetches a presigned download URL from the backend.
+  Future<String?> resolve(String? imageUrl) async {
+    if (imageUrl == null || imageUrl.isEmpty) return null;
+    if (imageUrl.startsWith('http://') || imageUrl.startsWith('https://')) {
+      return imageUrl;
+    }
+
+    // Check cache
+    if (_cache.containsKey(imageUrl)) return _cache[imageUrl];
+
+    // Deduplicate in-flight requests for the same key
+    if (_pending.containsKey(imageUrl)) return _pending[imageUrl];
+
+    final future = _fetchPresignedUrl(imageUrl);
+    _pending[imageUrl] = future;
+
+    try {
+      final result = await future;
+      if (result != null) _cache[imageUrl] = result;
+      return result;
+    } finally {
+      _pending.remove(imageUrl);
+    }
+  }
+
+  Future<String?> _fetchPresignedUrl(String key) async {
+    try {
+      final response = await ApiClient.instance.dio.get(
+        '/upload/presigned-download-url',
+        queryParameters: {'key': key},
+      );
+      final data = response.data;
+      // Backend wraps: { success: true, data: { url: "..." } }
+      if (data is Map<String, dynamic>) {
+        final payload = data['data'];
+        if (payload is Map<String, dynamic>) {
+          return payload['url'] as String?;
+        }
+        // In case response isn't wrapped (direct controller return)
+        return data['url'] as String?;
+      }
+      return null;
+    } on DioException {
+      return null;
+    }
+  }
+
+  void clearCache() => _cache.clear();
+}