feat: 装配切换——main/服务构造线/conftest 迁至 Registry（含默认租户过渡兜底）

- main.py: 删全局 engine/async_session;lifespan 装配 TenantRegistry
  (seed_profiles → 仓库根 tenants/,路径锚定),预热默认租户 jiancai 挂
  app.state.default_runtime,逐 active 租户(库文件已存在)跑
  sweep_stale_pending,退出 dispose_all。app.state.registry 预置即沿用
  (测试注入缝)
- routes/runtime.py(过渡,Task 7 删): get_runtime——state.tenant 优先,
  缺省落 default_runtime;chat.py/chat_rest.py 全部改走它,消除
  main↔routes 循环依赖
- ConversationManager 构造线: 新增 runtime 可选参(持 session_factory/
  compiled_wall/config 引用;prompts 仍模块级,Task 6;业务接线 Task 9),
  fire_pending_pushes 随任务传 session_factory(后台写回派发租户的库)
- lead_push_service: 去 app.main import;写库入口显式收 session_factory,
  模块级 async_session=None 仅作测试注入兜底
- conftest: client 夹具 = 每测试独立 Registry(tmp data_dir)+ 真实
  lifespan 在 TestClient 循环内预热;删 _dispose_main_engine;
  async_db 保持 NullPool(跨 asyncio.run 循环安全,刻意不换 Registry 引擎)
- 测试仅动夹具/桩签名(断言零改动): wiring 桩补 session_factory 形参;
  history-404 用例改经真实 WS 路由造 widget 会话(引擎常驻连接绑定
  TestClient 循环,测试线程不得直开 session_factory)

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

tests/test_lead_push_wiring.py

@@ -50,7 +50,7 @@ def _setup(async_db, monkeypatch, ai, lead_succeeds=True):
 
     fired = []
     monkeypatch.setattr(lead_push_service, "fire_pending_pushes",
-                        lambda logs: fired.extend(logs))
+                        lambda logs, session_factory=None: fired.extend(logs))
     monkeypatch.setattr(lead_push_service.settings, "PUSH_ENABLED", True)
 
     async def run():
@@ -165,7 +165,7 @@ def test_push_disabled_writes_nothing(async_db, monkeypatch):
     monkeypatch.setattr(email_service, "send_lead_email", fake_lead)
     fired = []
     monkeypatch.setattr(lead_push_service, "fire_pending_pushes",
-                        lambda logs: fired.extend(logs))
+                        lambda logs, session_factory=None: fired.extend(logs))
 
     async def run():
         async with async_db() as db:
@@ -183,7 +183,7 @@ def test_fire_end_to_end_single_loop(async_db, monkeypatch):
     """真 fire + 假 _run_push: 同一事件循环内 stream 完成后任务确实被派发执行。"""
     pushed = []
 
-    async def fake_run(log_id, payload):
+    async def fake_run(log_id, payload, session_factory=None):
         pushed.append(log_id)
 
     monkeypatch.setattr(lead_push_service, "_run_push", fake_run)
@@ -234,7 +234,7 @@ def test_fire_happens_only_after_commit(async_db, monkeypatch):
         sent.append("lead")
         return True
 
-    async def fake_run(log_id, payload):
+    async def fake_run(log_id, payload, session_factory=None):
         async with async_db() as db:
             try:
                 row = (await db.execute(
@@ -249,9 +249,9 @@ def test_fire_happens_only_after_commit(async_db, monkeypatch):
 
     real_fire = lead_push_service.fire_pending_pushes
 
-    def recording_fire(logs):
+    def recording_fire(logs, session_factory=None):
         fired.append(True)
-        real_fire(logs)
+        real_fire(logs, session_factory)
 
     monkeypatch.setattr(email_service, "send_lead_email", fake_lead)
     monkeypatch.setattr(lead_push_service, "_run_push", fake_run)