feat: TenantSource 抽象——File源(测试/档案)与DB源(生产)，registry 数据源可切换+reload upsert

Co-Authored-By: Claude Code <noreply@anthropic.com>

tests/test_host_routing.py

@@ -16,13 +16,12 @@ from app.platform.host_middleware import TenantHostMiddleware
 from tests.conftest import (
     AUTO_HOST,
     JIANCAI_HOST,
+    NOPE_HOST,
     SEED_DIR,
     app_test_client,
     build_app,
 )
 
-NOPE_HOST = "nope.example.com"
-
 
 # ---- 中间件挂载顺序守护 -------------------------------------------------------