refactor: 统一 Redis 连接管理，改用 RedisService

- App 启动时初始化 RedisService，关闭时释放连接
- Celery worker 通过 worker_process_init 钩子初始化 Redis
- Agent 端点改用 RedisService 替代直接创建连接
- Celery task 改为 async def，使用统一连接
- 删除无用的 infra 模块和 core/http/models
- 日志脱敏，不记录 Redis 密码
- 初始化失败时 fail-fast
- 异常发布添加二级保护

backend/tests/integration/test_mobile_app_skeleton.py

@@ -15,16 +15,6 @@ def test_app_health_returns_envelope() -> None:
     assert body["status"] == "ok"
 
 
-def test_mobile_router_health_returns_envelope() -> None:
-    client = TestClient(app)
-
-    response = client.get("/api/v1/health")
-
-    assert response.status_code == 200
-    body = response.json()
-    assert body["status"] == "ok"
-
-
 def test_not_found_returns_error_envelope() -> None:
     client = TestClient(app)