fix(config): update stale comment from bird CLI to twitter-cli

[YUHAO-corn]

Summary / 问题说明

config.py line 24 still references bird CLI in a comment, but the project has migrated to twitter-cli. This is the same class of stale reference as #282, just in code instead of docs.

config.py 第 24 行的注释仍然写着 bird CLI，但项目已经迁移到 twitter-cli。和 #282 是同类问题，只是出现在代码注释里。

Changes / 改动

# before
"twitter_xreach": ["twitter_auth_token", "twitter_ct0"],  # legacy key name; used by bird CLI

# after
"twitter_xreach": ["twitter_auth_token", "twitter_ct0"],  # legacy key name; used by twitter-cli

Test / 测试

All 85 tests pass (python3 -m pytest tests/ -v).

Related / 关联

Related to #282