refactor: worker 子系统全面异步化，拆掉同步转异步的桥接层

拆掉「同步调异步 / 异步桥同步」两类垫片的第二半（HTTP 线 B2 见前序提交）。
worker 侧此前是「起线程跑同步函数、函数体内部再用 asyncio.to_thread 把活塞给
另一条循环」——线程与协程互等，取消/暂停只能靠轮询。本轮把 worker 自身变成
协程，由 _start_task 直接挂到应用事件循环上，桥接层随之失去存在理由。

改动（按子系统）：
- music_downloader：downloader / _aria2 / _concurrency / cover / _http /
  __main__ 全链路协程化。per-file 锁改 asyncio.Lock；计数闸改
  「active 计数 + await asyncio.sleep(0.5)」的可取消等待（原阻塞式 with 会让
  已取消任务仍要等全局名额腾出，卡死并拖后腿退款）；aria2p 的同步 RPC 仍经
  to_thread，轮询改 asyncio.sleep；新增 core.http_client.iter_chunks，把**流式
  读取期**的 aiohttp.ClientError 收敛成 UpstreamNetworkError（请求建立阶段早已
  有这条路径，读取阶段此前没有，断流会绕过调用方的 UpstreamError 分类）。
  删除 get_http_session / _SESSION_LOCAL。
  models._RetryFromScratch 不再继承 requests.RequestException 而继承 Exception：
  它是「续传起点失效、残片已清、从头重下」，既不是确定性失败
  (DownloadException)，也不是残片已保留的网络失败(UpstreamError)，必须独立
  成类且在 except 链中先于二者捕获。
- music_api：podcast.py 全部函数协程化（直链解析内部改
  await NeteaseAPI.get_song_url）；compat.py 删除——16 个死掉的同步门面早已
  清空，文件只剩空壳。
- services：_taskcore / _zipcore / batch / downloads / podcast / tasks 协程化。
  threading.Thread → loop.create_task（任务句柄字段 worker_thread →
  worker_task），ThreadPoolExecutor → asyncio.gather + asyncio.Semaphore，
  终态函数与结算回调全部改 await；监控线程里「worker 已死」判定改 task.done()。
  删除 services/streaming.py（同步流垫片，唯一消费者已迁到
  core.http_client.open）。zipfile 实例仍非线程安全，故「下载」并行、
  「入包」严格串行。
- web：路由层 130+ 处 to_thread 拆除——被包住的目标自己已是协程，再包一层只是
  把协程丢进线程里跑一圈。tasks_registry.start_task 直接 create_task。
  web/app.py 关闭段去掉 async_bridge.shutdown()（不再有第二条约循环）。
  web/routers/download.py 的播客端点补上 3 处漏掉的 await
  （extract_podcast_ref / get_radio_detail）——漏掉时不报错、只静默返回协程对象，
  靠 pyright 抓出来后修正。

留在 to_thread 上的都是**正当的阻塞卸载**：同步 SQLite 落库与账本结算、
mutagen 全量重写标签、zipfile 整段拷贝、shutil.rmtree、aria2p 的同步 RPC、
PBKDF2 的 10 万次迭代。ruff 对残留的本地元数据操作（exists/stat/os.replace/
往 .part 顺序写分块）按「微秒级、卸载的调度开销大于操作本身」放行，pyproject
逐条注明理由。

取消/暂停仍由 threading.Event 承载：置位方是请求线程/监控线程，读取方是 worker
协程，只有「置位」与「轮询读取」两种操作，既不需要跨循环唤醒也不会卡住事件
循环——比 asyncio.Event 更省心（ASYNC110 同理按此豁免）。

测试：10 个文件的替身边界同步迁移——网络替身从 core.sync_http 的
get_http_session 换成 downloader/服务模块的 _http.open + **真实** iter_chunks
（顺带钉住读取期异常收敛）；`_run` 改为在独立线程里 asyncio.run(worker(...))；
aria2 的假时钟从 time.sleep 换成 _POLL_INTERVAL=0；monitor 的线程句柄替身换成
done() 可控的轻量替身（asyncio.Task 的构造需要运行中的事件循环，而监控循环跑在
常驻线程里）；podcast / 封面 / 结算包装等替身一律改 async。

门禁：ruff 全过 / pyright 0-0 / pytest 383 项全绿（0 失败）。

下一步 B2：auth_system 12 个模块改 aiosqlite 背板、web 层剩余 to_thread 收尾；
B3：删 core/sync_http.py、core/async_bridge.py、core/http_errors.py（现仅
sync_http 自用）。

tests/test_resolve_episode_url.py

@@ -8,8 +8,9 @@
 - 未知音质 → 该音质优先 + 通用阶梯
 - song_id 垃圾值 → None 且不发任何请求
 
-替身边界：monkeypatch ``podcast.url_v1``（模块级名字，podcast.py 从
-.compat 导入后的绑定），按 level 返回结果或抛异常，并记录调用序列。
+替身边界：monkeypatch ``music_api.podcast.NeteaseAPI``——resolve_episode_url 内部
+现构造该客户端并 ``await api.get_song_url(...)``，替身按 level 返回结果或抛异常，
+并记录调用序列。
 """
 import pytest
 
@@ -23,14 +24,18 @@ def url_calls(monkeypatch):
     calls: list[tuple[int, str]] = []
     state: dict = {'results': {}}
 
-    def _fake_url_v1(sid, level, cookies):
+    async def _fake_get_song_url(sid, level, cookies):
         calls.append((sid, level))
         r = state['results'].get(level)
         if isinstance(r, Exception):
             raise r
         return r
 
-    monkeypatch.setattr(podcast_mod, 'url_v1', _fake_url_v1)
+    class _FakeAPI:
+        async def get_song_url(self, sid, level, cookies):
+            return await _fake_get_song_url(sid, level, cookies)
+
+    monkeypatch.setattr(podcast_mod, 'NeteaseAPI', _FakeAPI)
     state['calls'] = calls
     return state
 
@@ -42,38 +47,38 @@ def _ok(level: str = 'standard') -> dict:
 
 async def test_auto_tries_quality_ladder_in_order(url_calls):
     """auto：按 QUALITY_LADDER 原序尝试，全失败返回 None。"""
-    assert resolve_episode_url(101, {}, 'auto') is None
+    assert await resolve_episode_url(101, {}, 'auto') is None
     assert url_calls['calls'] == [(101, 'exhigh'), (101, 'standard')]
 
 
 async def test_explicit_level_falls_down_only(url_calls):
     """显式 lossless：向后降级 exhigh/standard，绝不向上尝试 hires。"""
-    assert resolve_episode_url(101, {}, 'lossless') is None
+    assert await resolve_episode_url(101, {}, 'lossless') is None
     assert url_calls['calls'] == [(101, 'lossless'), (101, 'exhigh'), (101, 'standard')]
 
 
 async def test_standard_never_falls_up(url_calls):
     """显式 standard：只试一次（历史坑：原实现会回退到更高的 exhigh）。"""
-    assert resolve_episode_url(101, {}, 'standard') is None
+    assert await resolve_episode_url(101, {}, 'standard') is None
     assert url_calls['calls'] == [(101, 'standard')]
 
 
 async def test_unknown_level_prepends_generic_ladder(url_calls):
     """未知音质：先试该音质，再退通用阶梯（去重保序）。"""
-    assert resolve_episode_url(101, {}, 'sky') is None
+    assert await resolve_episode_url(101, {}, 'sky') is None
     assert url_calls['calls'] == [(101, 'sky'), (101, 'exhigh'), (101, 'standard')]
 
 
 async def test_first_hit_returns_mapped_result(url_calls):
     url_calls['results']['exhigh'] = _ok('hires')
-    out = resolve_episode_url(101, {}, 'auto')
+    out = await resolve_episode_url(101, {}, 'auto')
     assert out == {'url': 'https://x/1.mp3', 'level': 'hires', 'type': 'mp3',
                    'size': 123, 'br': 128000, 'md5': 'abc', 'requested_level': 'exhigh'}
 
 
 async def test_level_defaults_to_requested_when_missing(url_calls):
     url_calls['results']['exhigh'] = {'data': [{'url': 'https://x/1.mp3'}]}
-    out = resolve_episode_url(101, {}, 'auto')
+    out = await resolve_episode_url(101, {}, 'auto')
     assert out is not None
     assert out['level'] == 'exhigh'
     assert out['type'] == 'mp3'
@@ -84,7 +89,7 @@ async def test_level_defaults_to_requested_when_missing(url_calls):
 async def test_api_exception_tries_next_level(url_calls):
     url_calls['results']['exhigh'] = APIException('无版权')
     url_calls['results']['standard'] = _ok()
-    out = resolve_episode_url(101, {}, 'auto')
+    out = await resolve_episode_url(101, {}, 'auto')
     assert out is not None
     assert out['requested_level'] == 'standard'
     assert url_calls['calls'] == [(101, 'exhigh'), (101, 'standard')]
@@ -94,7 +99,7 @@ async def test_missing_url_tries_next_level(url_calls):
     """data[0] 无 url：视同失败，继续降级。"""
     url_calls['results']['exhigh'] = {'data': [{'url': None}]}
     url_calls['results']['standard'] = _ok()
-    out = resolve_episode_url(101, {}, 'auto')
+    out = await resolve_episode_url(101, {}, 'auto')
     assert out is not None
     assert out['requested_level'] == 'standard'
 
@@ -102,7 +107,7 @@ async def test_missing_url_tries_next_level(url_calls):
 async def test_empty_data_tries_next_level(url_calls):
     url_calls['results']['exhigh'] = None  # res 为 None → data 为 []
     url_calls['results']['standard'] = _ok()
-    out = resolve_episode_url(101, {}, 'auto')
+    out = await resolve_episode_url(101, {}, 'auto')
     assert out is not None
     assert out['requested_level'] == 'standard'
 
@@ -110,12 +115,12 @@ async def test_empty_data_tries_next_level(url_calls):
 async def test_bad_song_id_returns_none_without_requests(url_calls):
     """song_id 垃圾值：None，且不发任何请求（防御原 TypeError 500）。"""
     for bad in (None, 'abc', ''):
-        assert resolve_episode_url(bad, {}, 'auto') is None
+        assert await resolve_episode_url(bad, {}, 'auto') is None
     assert url_calls['calls'] == []
 
 
 async def test_numeric_string_song_id_accepted(url_calls):
     url_calls['results']['exhigh'] = _ok()
-    out = resolve_episode_url(' 101 ', {}, 'auto')
+    out = await resolve_episode_url(' 101 ', {}, 'auto')
     assert out is not None
     assert url_calls['calls'][0] == (101, 'exhigh')