fix: avatar list fixes — full-width table, absolute photo URLs, global token balance

- Table width set to 100%
- Photo URLs resolved to absolute paths using AVATAR_BACKEND_URL
- Token balance now reads from global token_account table
- Config: added AVATAR_BACKEND_URL setting

backend/app/core/config.py

@@ -28,6 +28,9 @@ class Settings(BaseSettings):
     # 数字分身 SQLite 数据库路径（直连数字分身应用的 SQLite）
     AVATAR_DB_PATH: str = os.getenv("AVATAR_DB_PATH", "")
 
+    # 数字分身后端服务地址（用于拼接头像等文件 URL）
+    AVATAR_BACKEND_URL: str = os.getenv("AVATAR_BACKEND_URL", "")
+
     # 日志目录
     LOG_DIR: str = "/app/logs"