refactor(favsort): send bilibili requests through httpx

Reuse a pooled httpx client for favsort GET and POST requests, share the raw-request-derived browser headers, and add folder-specific referers for ids, infos and sort. Add transport tests for header parity and anonymous-to-authenticated fallback.

README.md

@@ -275,6 +275,7 @@ sort=A:2:B:2  →  将 B 插到 A 之后
 ```powershell
 uv run python tests/test_auth.py            # Cookie 合并、设备指纹、Set-Cookie 解析
 uv run python tests/test_moves.py           # 排序移动脚本：随机排列与头部用例
+uv run python tests/test_favsort_http.py    # favsort httpx 请求头与匿名回退
 uv run python tests/test_config.py          # 配置加载、校验、ENV 覆盖与热加载
 uv run python tests/test_migrations.py      # 迁移、备份、回滚与保留期
 uv run python tests/test_database.py        # 单写队列、事务与并发