refactor: 拆分 4 个巨石模块为包，清理过时注释并删除作废文档

为什么：单文件 1100~1900 行的巨石模块让「改一处要通读全文」；同时注释里残留
大量已删台账的编号，以及「Flask/FastAPI 双栈迁移期」这类已失实的架构描述，
会误导后来者按不复存在的架构去改代码。

拆分（对外导入路径不变，行为零变更）：
- music_downloader.py  -> music_downloader/（models/downloader/cover/_http/_log/_concurrency）
- auth_system.py       -> auth_system/（db/security/users/credits/ledger/mail/cards/backup...）
- music_api.py         -> music_api/（api/client/crypto/qr/cookies/compat/constants/errors）
- services/runtime.py  -> services/（api_service/_shared/_taskcore/downloads/batch/podcast/
  streaming/tasks）；services/runtime.py 保留为兼容门面

兼容性做法：各包用 __init__.py 以 __all__ 原样再导出全部符号，既有调用点
（auth_system.xxx / services.xxx / from music_api import Y）零改动；路径常量改为经包属性
动态读取（auth_system.DB_PATH），否则测试的 monkeypatch 会静默失效并写到生产库。

修复 9 处代码损伤（上一轮注释清理把 `()` 当「空括号残留」删掉所致；用「与拆分前逐字
等价」校验逐一定位，静态检查只会报出其中 4 处）：
- core/config.py  ).strip() or '*'
- core/state.py   threading.Lock() x2
- qr_login.py     datetime.now() / .strip()
- music_downloader/downloader.py  .lower()
- services/podcast.py  set() / time.time() x2

清理与删除：
- 删除 部署文档.md / 功能介绍.md / README_私有包警告.txt
- 清理指向已删台账与文档的过时编号注释；把「迁移期 / 两栈 / 双框架 / 已迁移」等
  失实描述改写为现状描述（保留 `<-> Flask /path` 映射表等仍有价值的契约来源说明）
- _mkpkg.py：公开包剔除清单去掉已不存在的文档名；私有包警告改为自包含
- pyproject.toml：补 pythonpath = ["."]，使裸跑 pytest 不再 import core 失败

验证：ruff 全通过；pyright 0 errors / 0 warnings（102 文件）；pytest 144 passed；
真实 uvicorn 冒烟 6 条路由符合预期且生产 data/ 指纹未变；忽略注释的逐字等价性校验通过。

music_api/compat.py

@@ -0,0 +1,128 @@
+# -*- coding: utf-8 -*-
+"""同步兼容函数接口（内部经 run_sync 桥接异步实现）。
+
+（自 music_api.py 拆出，行为与原实现一致。）
+"""
+
+from typing import Any
+
+from core.async_bridge import run_sync  # 模块级同步兼容接口用的同步/异步桥
+
+from .api import (
+    NeteaseAPI,
+)
+from .qr import (
+    QRLoginManager,
+)
+
+
+# 向后兼容的函数接口
+def url_v1(song_id: int, level: str, cookies: dict[str, str]) -> dict[str, Any]:
+    """获取歌曲URL（向后兼容）"""
+    api = NeteaseAPI()
+    return run_sync(api.get_song_url(song_id, level, cookies))
+
+
+def name_v1(song_id: int) -> dict[str, Any]:
+    """获取歌曲详情（向后兼容）"""
+    api = NeteaseAPI()
+    return run_sync(api.get_song_detail(song_id))
+
+
+def lyric_v1(song_id: int, cookies: dict[str, str]) -> dict[str, Any]:
+    """获取歌词（向后兼容）"""
+    api = NeteaseAPI()
+    return run_sync(api.get_lyric(song_id, cookies))
+
+
+def search_music(keywords: str, cookies: dict[str, str], limit: int = 10,
+                 search_type: int = 1, offset: int = 0) -> list[dict[str, Any]]:
+    """搜索音乐（向后兼容）"""
+    api = NeteaseAPI()
+    return run_sync(api.search_music(keywords, cookies, limit, search_type, offset=offset))
+
+
+def toplist_list() -> list[dict[str, Any]]:
+    """获取官方榜单列表（向后兼容）"""
+    api = NeteaseAPI()
+    return run_sync(api.get_toplist())
+
+
+def artist_songs(artist_id: int) -> dict[str, Any]:
+    """获取歌手信息和热门歌曲（向后兼容）"""
+    api = NeteaseAPI()
+    return run_sync(api.get_artist_hot_songs(artist_id))
+
+
+def song_comments(song_id: int, limit: int = 20, offset: int = 0) -> dict[str, Any]:
+    """获取歌曲评论（向后兼容）"""
+    api = NeteaseAPI()
+    return run_sync(api.get_song_comments(song_id, limit, offset))
+
+
+def account_info(cookies: dict[str, str]) -> dict[str, Any] | None:
+    """获取当前账号信息（向后兼容）"""
+    api = NeteaseAPI()
+    return run_sync(api.get_account_info(cookies))
+
+
+def user_playlists(user_id: int, cookies: dict[str, str]) -> list[dict[str, Any]]:
+    """获取用户收藏/创建的歌单列表（向后兼容）"""
+    api = NeteaseAPI()
+    return run_sync(api.get_user_playlists(user_id, cookies))
+
+
+def detect_vip_by_probe(cookies: dict[str, str], probe_song_id: int = 347230) -> dict[str, Any]:
+    """通过歌曲URL接口探测账号会员类型（向后兼容）"""
+    api = NeteaseAPI()
+    return run_sync(api.detect_vip_by_probe(cookies, probe_song_id))
+
+
+def playlist_subscribe(playlist_id: int, cookies: dict[str, str], action: int = 1) -> dict[str, Any]:
+    """收藏/取消收藏歌单（向后兼容）"""
+    api = NeteaseAPI()
+    return run_sync(api.subscribe_playlist(playlist_id, cookies, action))
+
+
+def album_subscribe(album_id: int, cookies: dict[str, str], action: int = 1) -> dict[str, Any]:
+    """收藏/取消收藏专辑（向后兼容）"""
+    api = NeteaseAPI()
+    return run_sync(api.subscribe_album(album_id, cookies, action))
+
+
+def post_comment(thread_id: str, content: str, action: int = 1,
+                 comment_id: int | None = None,
+                 cookies: dict[str, str] | None = None) -> dict[str, Any]:
+    """发送/回复歌曲评论（向后兼容）"""
+    api = NeteaseAPI()
+    return run_sync(api.post_comment(thread_id, content, action, comment_id, cookies))
+
+
+def probe_levels(cookies: dict[str, str], probe_song_id: int = 347230) -> list[str]:
+    """实测账号可解析的音质列表（向后兼容）"""
+    api = NeteaseAPI()
+    return run_sync(api.probe_levels(cookies, probe_song_id))
+
+
+def playlist_detail(playlist_id: int, cookies: dict[str, str]) -> dict[str, Any]:
+    """获取歌单详情（向后兼容）"""
+    api = NeteaseAPI()
+    return run_sync(api.get_playlist_detail(playlist_id, cookies))
+
+
+def album_detail(album_id: int, cookies: dict[str, str]) -> dict[str, Any]:
+    """获取专辑详情（向后兼容）"""
+    api = NeteaseAPI()
+    return run_sync(api.get_album_detail(album_id, cookies))
+
+
+def get_pic_url(pic_id: int | None, size: int = 300) -> str:
+    """获取图片URL（向后兼容）"""
+    api = NeteaseAPI()
+    return api.get_pic_url(pic_id, size)
+
+
+def qr_login() -> str | None:
+    """二维码登录（向后兼容）"""
+    manager = QRLoginManager()
+    return run_sync(manager.qr_login())