fix(architecture): move media auxiliary mixin into _base package

media_auxiliary 作为模块共享 Mixin 放在 app/modules 顶层会被视为
业务模块，导致 anilist/bangumi/douban/imdb/themoviedb 跨模块直接
依赖，违反模块间禁止导入的架构约束。移入模块共享样板包
app/modules/_base（模块发现跳过）并同步依赖基线。

app/modules/douban/__init__.py

@@ -21,7 +21,7 @@ from app.foundation.text import convert as zhconv_convert
 from app.modules import _ModuleBase
 from app.modules.douban.apiv2 import DoubanApi
 from app.modules.douban.scraper import DoubanScraper
-from app.modules.media_auxiliary import MediaAuxiliaryProviderMixin
+from app.modules._base.media_auxiliary import MediaAuxiliaryProviderMixin
 from app.runtime.execution import retry
 from app.runtime.log import logger
 from app.runtime.rate import rate_limit_exponential