make a media api, encapsulate the original S3 bucket address

there are 3 parts, from back to head, url inside the bucket -> url of backend media api -> backend domain, only the last part is spliced by frontend, the other two parts are spliced with sqlalchemy

app/models/user.py

@@ -17,6 +17,19 @@ class User(Base, AutoID):
     handle = Column(String, unique=True, index=True, nullable=True)
     avatar = Column(String)
     
+    @property
+    def avatar_url(self) -> str | None:
+        if not self.avatar:
+            return None
+            
+        # 如果是第三方（如未迁移成功时降级的 Google 原始链接），直接返回
+        if self.avatar.startswith(("http://", "https://")):
+            return self.avatar
+        
+        path = self.avatar.lstrip("/")
+        
+        return f"/v1/media/{path}"
+    
     # ---- 互动统计字段 ----
     following_count = Column(Integer, default=0, nullable=False, server_default="0")            # 关注了多少人
     follower_count = Column(Integer, default=0, nullable=False, server_default="0")             # 粉丝数