refactor: 删除 services.runtime 兼容门面，7 处调用点直连真实子模块

为什么：上一次分包重构把 1900 行巨石按职责拆成 9 个子模块后，留了一个
runtime.py 作为「原样再导出」的兼容门面，好让调用点零改动。但迁移期结束后
没有一个调用点迁走——门面成了永久中间层：每次读代码都要先跳一层才知道
符号真正住在哪，pyright 也无法从门面追溯定义位置。

改法：保持「函数内延迟导入」的形式不变，只把导入目标换成真实子模块。
**刻意不提到模块顶部**——services/__init__.py 里有依赖自检
（缺 auth_system/podcast_api/music_api/music_downloader/qr_login 就 sys.exit(1)），
提到顶层会让「import web.*」这一步就触发该自检，改变启动语义，超出本次范围。

7 处调用点（AST 精确扫描确认全集）：
- web/routers/download.py ×4：download / download_batch_zip / podcast_download /
  podcast_batch_zip，分别直连 services.downloads / batch / podcast / tasks
  外加 _shared._build_download_base 与 api_service.api_service
- web/routers/tasks.py ×2：_semaphores 取 _shared.BATCH_ZIP_SEM + api_service，
  topen 取 _shared.ENDPOINT_NAMES
- web/tasks_registry.py ×1：start_task 直连 _taskcore._start_task_thread

子模块短名统一加 `services_` 前缀别名（services_tasks 等），避免与函数内
既有局部名相撞。

顺带清理：9 个子模块 docstring 里「（自 services/runtime.py 拆出……）」的
历史说明在门面删除后已成悬空引用，一并去掉；包的模块划分说明改为
「不再有兼容门面层」。

验证：
- 符号可达：11 个被引符号在真实子模块上全部 hasattr 通过；
  services.runtime 已 ModuleNotFoundError；api_service 仍是同一实例对象
- 三个调用方模块均可正常 import
- 门禁：ruff 0 · pyright 0 errors 0 warnings · pytest 175 passed
- 真实 uvicorn 冒烟 8/8（含 POST /auth/login 400），临时数据目录独立落库
  9 张表，生产 data/ 指纹三项一致

web/routers/download.py

@@ -115,8 +115,11 @@ async def download(user: Annotated[SiteUser | None, Depends(current_user)], requ
             lyric_format = 'lrc'
         need_zip = str(data.get('zip', 'false')).lower() in ('1', 'true', 'yes')
 
-        import services.runtime as services
-        downloader = services.api_service.downloader
+        from services import downloads as services_downloads
+        from services import tasks as services_tasks
+        from services._shared import _build_download_base
+        from services.api_service import api_service
+        downloader = api_service.downloader
 
         if return_format == 'json':
             try:
@@ -127,7 +130,7 @@ async def download(user: Annotated[SiteUser | None, Depends(current_user)], requ
                 await billing.refund_open('rejected')
                 return error('获取失败：歌曲不存在或暂无版权', 404)
             base = await asyncio.to_thread(
-                services._build_download_base, filename_format,
+                _build_download_base, filename_format,
                 {'name': info.name, 'artist_string': info.artists})
             filename = f'{base}.{info.file_type}'
             try:
@@ -165,7 +168,7 @@ async def download(user: Annotated[SiteUser | None, Depends(current_user)], requ
 
         # file 模式：注册后台任务
         device_id = str(data.get('device_id') or '').strip()[:64]
-        await asyncio.to_thread(services._touch_device, device_id)
+        await asyncio.to_thread(services_tasks._touch_device, device_id)
         task = _single_task(data, music_id, quality, filename_format, write_meta,
                             meta_fields, lyric_format, need_zip, cookies, ip, device_id)
         reg_err = await register_download_task(billing, task, str(data.get('task_id') or '').strip())
@@ -173,7 +176,7 @@ async def download(user: Annotated[SiteUser | None, Depends(current_user)], requ
             await billing.refund_open('rejected')
             return error(reg_err, 429)
         task_id = task['task_id']
-        start_err = await start_task(task_id, services._single_download_worker, (task_id,))
+        start_err = await start_task(task_id, services_downloads._single_download_worker, (task_id,))
         if start_err:
             return error(start_err, 500)
         return success({'task_id': task_id, 'status': 'queued'}, '下载任务已提交')
@@ -248,8 +251,9 @@ async def download_batch_zip(user: Annotated[SiteUser | None, Depends(current_us
 
         cookies = _cookies()
         device_id = str(data.get('device_id') or '').strip()[:64]
-        import services.runtime as services
-        await asyncio.to_thread(services._touch_device, device_id)
+        from services import batch as services_batch
+        from services import tasks as services_tasks
+        await asyncio.to_thread(services_tasks._touch_device, device_id)
         task = {
             'type': 'batch',
             'total': len(ids), 'done': 0, 'failed': 0,
@@ -269,7 +273,7 @@ async def download_batch_zip(user: Annotated[SiteUser | None, Depends(current_us
             await billing.refund_open('rejected')
             return error(reg_err, 429)
         task_id = task['task_id']
-        start_err = await start_task(task_id, services._batch_zip_worker, (task_id,))
+        start_err = await start_task(task_id, services_batch._batch_zip_worker, (task_id,))
         if start_err:
             return error(start_err, 500)
         return success({'task_id': task_id, 'status': 'queued', 'total': len(ids)},
@@ -330,8 +334,9 @@ async def podcast_download(user: Annotated[SiteUser | None, Depends(current_user
             cookies = _cookies()
 
         device_id = str(data.get('device_id') or '').strip()[:64]
-        import services.runtime as services
-        await asyncio.to_thread(services._touch_device, device_id)
+        from services import podcast as services_podcast
+        from services import tasks as services_tasks
+        await asyncio.to_thread(services_tasks._touch_device, device_id)
         task = {
             'type': 'single',
             'total': 1, 'done': 0, 'failed': 0,
@@ -346,7 +351,7 @@ async def podcast_download(user: Annotated[SiteUser | None, Depends(current_user
             await billing.refund_open('rejected')
             return error(reg_err, 429)
         task_id = task['task_id']
-        start_err = await start_task(task_id, services._podcast_download_worker, (task_id,))
+        start_err = await start_task(task_id, services_podcast._podcast_download_worker, (task_id,))
         if start_err:
             return error(start_err, 500)
         return success({'task_id': task_id, 'status': 'queued'}, '播客单集下载任务已提交')
@@ -405,8 +410,9 @@ async def podcast_batch_zip(user: Annotated[SiteUser | None, Depends(current_use
 
         billed = _podcast_billing_count(data)
         device_id = str(data.get('device_id') or '').strip()[:64]
-        import services.runtime as services
-        await asyncio.to_thread(services._touch_device, device_id)
+        from services import podcast as services_podcast
+        from services import tasks as services_tasks
+        await asyncio.to_thread(services_tasks._touch_device, device_id)
         task = {
             'type': 'batch',
             'total': 0, 'done': 0, 'failed': 0,
@@ -428,7 +434,7 @@ async def podcast_batch_zip(user: Annotated[SiteUser | None, Depends(current_use
             await billing.refund_open('rejected')
             return error(reg_err, 429)
         task_id = task['task_id']
-        start_err = await start_task(task_id, services._podcast_zip_worker, (task_id,))
+        start_err = await start_task(task_id, services_podcast._podcast_zip_worker, (task_id,))
         if start_err:
             return error(start_err, 500)
         return success({'task_id': task_id, 'status': 'queued'}, '播客打包任务已提交')