feat(liblogc): 统一集中式日志客户端库 + 全量迁移

新增:
- liblogc/: C++ 统一日志库 (libus_logc.so)，支持 set_endpoint/set_service_name/set_level
- pymsg/pymsg/logc.py: Python 统一日志模块，基于 AsyncRpcQueue

C++ 迁移 (删除 6 份本地 LogC.hpp 副本):
- ca, gateway: <us/LogC.hpp> + set_service_name
- captcha2, confs2, smtp3: using qing::LogC + set_service_name
- core: ConfsLogC → qing::LogC (ConfsTask.cpp)
- 所有 Makefile 添加 -lus_logc

Python 迁移 (6 个 log_client.py → 4 行薄包装):
- smtp, redirect80, confs, captcha, dnfs, static
- 全部委托到 pymsg.logc.LogClient

Go (waf): 保持现状，自成体系

pymsg/pymsg/__init__.py

@@ -621,5 +621,7 @@ class MsgServer:
 # ── JSON RPC 约定层（依赖上面的 MsgClient / MsgServer，故放在末尾导入）──
 from .rpc import RpcClient, RpcError, RpcServer  # noqa: E402
 from .async_queue import AsyncRpcQueue  # noqa: E402
+from .logc import LogClient, set_log_level  # noqa: E402
 
-__all__ += ["RpcClient", "RpcServer", "RpcError", "AsyncRpcQueue"]
+__all__ += ["RpcClient", "RpcServer", "RpcError", "AsyncRpcQueue",
+            "LogClient", "set_log_level"]