refactor: 始终上传头像到服务器

- 前端始终上传头像到服务器，不再判断是否为临时路径
- 后端移除downloadAvatar方法
- 数据库avatar_url始终存储服务器路径

src/main/java/xuan/controller/UserController.java

@@ -10,8 +10,6 @@ import xuan.service.UserInfoService;
 
 import java.io.File;
 import java.io.IOException;
-import java.io.InputStream;
-import java.net.URL;
 import java.nio.file.Files;
 import java.nio.file.Path;
 import java.nio.file.Paths;
@@ -66,12 +64,7 @@ public class UserController {
                 openId = "guest_" + System.currentTimeMillis();
             }
             
-            String localAvatarUrl = avatarUrl;
-            if (avatarUrl != null && !avatarUrl.isEmpty() && avatarUrl.startsWith("http")) {
-                localAvatarUrl = downloadAvatar(avatarUrl, openId);
-            }
-            
-            UserInfo user = userInfoService.loginOrRegister(openId, username, localAvatarUrl);
+            UserInfo user = userInfoService.loginOrRegister(openId, username, avatarUrl);
             
             Map<String, Object> data = new HashMap<>();
             data.put("id", user.getId());
@@ -94,40 +87,6 @@ public class UserController {
         return result;
     }
     
-    private String downloadAvatar(String imageUrl, String userId) {
-        try {
-            String uploadDir = "uploads/avatars/";
-            File dir = new File(uploadDir);
-            if (!dir.exists()) {
-                dir.mkdirs();
-            }
-            
-            String extension = ".jpg";
-            if (imageUrl.contains(".")) {
-                String tempExt = imageUrl.substring(imageUrl.lastIndexOf("."));
-                if (tempExt.contains("?")) {
-                    tempExt = tempExt.substring(0, tempExt.indexOf("?"));
-                }
-                if (tempExt.length() <= 5 && tempExt.matches("\\.[a-zA-Z]+")) {
-                    extension = tempExt;
-                }
-            }
-            
-            String filename = userId + "_" + System.currentTimeMillis() + extension;
-            Path filePath = Paths.get(uploadDir + filename);
-            
-            URL url = new URL(imageUrl);
-            try (InputStream in = url.openStream()) {
-                Files.copy(in, filePath);
-            }
-            
-            return "/uploads/avatars/" + filename;
-        } catch (Exception e) {
-            System.err.println("下载头像失败: " + e.getMessage());
-            return imageUrl;
-        }
-    }
-    
     @GetMapping("/info")
     public Map<String, Object> getUserInfo(@RequestParam String userId) {
         Map<String, Object> result = new HashMap<>();