fix: 图片发送/医生加载/运动超时/用药黑屏/服药打卡

- sendImage: 本地预览→上传→远程URL替换
- doctorListProvider: 8s超时+mock医生fallback
- currentExercisePlanProvider: 8s超时→显示空状态
- 用药编辑: try-catch防黑屏+刷新列表
- 服药打卡: 接入后端confirm()接口

health_app/lib/core/api_client.dart

@@ -1,3 +1,4 @@
+import 'dart:io';
 import 'package:dio/dio.dart';
 import 'local_database.dart';
 
@@ -54,6 +55,19 @@ class ApiClient {
   Future<Response> delete(String path) async {
     return _dio.delete(path);
   }
+
+  /// 上传文件（multipart），返回文件 URL
+  Future<String?> uploadFile(String path, File file, {String fieldName = 'file'}) async {
+    final formData = FormData.fromMap({
+      fieldName: await MultipartFile.fromFile(file.path, filename: file.path.split('/').last),
+    });
+    final res = await _dio.post(path, data: formData);
+    final data = res.data;
+    if (data is Map) {
+      return data['url']?.toString() ?? data['data']?['url']?.toString();
+    }
+    return null;
+  }
 }
 
 /// 认证拦截器：自动注入 token + 401 刷新