Add file uploads for photos and family icons

flutter_app/lib/services/api_client.dart

@@ -1,4 +1,5 @@
 import "dart:convert";
+import "dart:typed_data";
 import "package:http/http.dart" as http;
 import "../config/api_config.dart";
 
@@ -45,6 +46,30 @@ class ApiClient {
     return jsonDecode(response.body) as Map<String, dynamic>;
   }
 
+  Future<Map<String, dynamic>> postMultipart(
+    String path, {
+    required String fieldName,
+    required Uint8List bytes,
+    required String filename,
+    Map<String, String>? fields,
+  }) async {
+    final request = http.MultipartRequest("POST", _uri(path));
+    if (fields != null) {
+      request.fields.addAll(fields);
+    }
+    request.files.add(
+      http.MultipartFile.fromBytes(
+        fieldName,
+        bytes,
+        filename: filename,
+      ),
+    );
+    final streamed = await _client.send(request);
+    final response = await http.Response.fromStream(streamed);
+    _ensureSuccess(response);
+    return jsonDecode(response.body) as Map<String, dynamic>;
+  }
+
   Future<Map<String, dynamic>> put(
     String path,
     Map<String, dynamic> body,