fix(plugin): 修复坏插件模块声明击穿模块调度导致接口大面积报错

- projection 只接受映射类型的 get_module 声明，非法值跳过并记日志
- dispatcher 同步/异步路径防御非映射方法表，单个坏插件被隔离
- media 端点改用 application 层插件运行时门面，消除分层违规依赖
- 图片能力测试打桩 models.dev 目录边界，适配仓库内离线目录留空

Closes #6346

app/api/endpoints/media.py

@@ -68,11 +68,11 @@ _BUILTIN_MEDIA_SOURCES = (
 
 def _registered_media_sources() -> list[_SchemaMediaSourceInfo]:
     """合并内置与启用插件声明的媒体来源，并按来源标识去重。"""
-    from app.runtime.extensions.plugin_manager import PluginManager
+    from app.application.plugin.runtime import get_plugin_manager
 
     result = list(_BUILTIN_MEDIA_SOURCES)
     seen = {source.media_source for source in result}
-    for raw_source in PluginManager().get_media_sources():
+    for raw_source in get_plugin_manager().get_media_sources():
         try:
             source = _SchemaMediaSourceInfo.model_validate(raw_source)
         except Exception: