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

liblogc/src/LogC.cpp

@@ -0,0 +1,141 @@
+/** LogC.cpp — 统一集中式日志客户端实现
+ *
+ * 包含 _send_batch（pymsg → db execute INSERT）和 _utc_now_iso（ISO 8601）。
+ * 编译为 libus_logc.so，运行时依赖 libus_msg.so。
+ */
+
+#include <us/LogC.hpp>
+
+#include <chrono>
+#include <cstdio>
+#include <ctime>
+#include <iostream>
+#include <memory>
+
+#include <boost/json.hpp>
+
+#include <us/AsyncQueue.hpp>
+#include <us/Msg.hpp>
+
+namespace json = boost::json;
+
+namespace qing {
+
+// ---- 生命周期 ---------------------------------------------------------------
+
+LogC::LogC()
+	: _queue(std::make_unique<pmc::net::AsyncQueue<Entry>>(
+		[this](std::vector<Entry>&& batch) { this->_send_batch(std::move(batch)); },
+		pmc::net::AsyncQueueConfig{_BATCH_SIZE, _FLUSH_INTERVAL, _MAX_QUEUE_SIZE, 0.5},
+		[](const std::exception& e, std::vector<Entry>&&) {
+			std::cerr << "[LogC] 发送失败: " << e.what() << std::endl;
+		}))
+{
+	_queue->start();
+}
+
+LogC::~LogC() { shutdown(); }
+
+// ---- 配置接口 ---------------------------------------------------------------
+
+void LogC::set_endpoint(const std::string& addr, int port) {
+	std::lock_guard<std::mutex> lock(_endpoint_mtx);
+	_db_addr = addr;
+	_db_port = port;
+}
+
+void LogC::set_service_name(const std::string& name) {
+	std::lock_guard<std::mutex> lock(_endpoint_mtx);
+	_service_name = name;
+}
+
+void LogC::set_level(const std::string& level) {
+	auto it = level_order().find(level);
+	if (it != level_order().end()) {
+		_level_threshold.store(it->second, std::memory_order_relaxed);
+	}
+}
+
+// ---- 推送 -------------------------------------------------------------------
+
+void LogC::push(const std::string& service, const std::string& level,
+		const std::string& message,
+		std::optional<std::string> trace_id,
+		std::optional<std::string> extra) {
+	auto it = level_order().find(level);
+	int lvl = (it != level_order().end()) ? it->second : 1;
+	if (lvl < _level_threshold.load(std::memory_order_relaxed)) return;
+	_queue->push(Entry{service, level, message,
+			std::move(trace_id), std::move(extra)});
+}
+
+void LogC::flush()    { _queue->flush(); }
+void LogC::shutdown() { _queue->shutdown(); }
+
+// ---- 内部实现 ---------------------------------------------------------------
+
+void LogC::_send_batch(std::vector<Entry>&& batch) {
+	std::string addr;
+	int port;
+	std::string client_name;
+	{
+		std::lock_guard<std::mutex> lock(_endpoint_mtx);
+		addr = _db_addr;
+		port = _db_port;
+		client_name = _service_name;
+	}
+
+	const std::string now = _utc_now_iso();
+	try {
+		pmc::net::MsgClient client(addr, port, client_name);
+		for (const auto& e : batch) {
+			json::object values;
+			values["ts"]       = now;
+			values["service"]  = e.service;
+			values["level"]    = e.level;
+			values["message"]  = e.message;
+			values["trace_id"] = e.trace_id ? json::value(*e.trace_id)
+					: json::value(nullptr);
+			values["extra"]    = e.extra ? json::value(*e.extra)
+					: json::value(nullptr);
+
+			json::object payload;
+			payload["_route"] = "execute";
+			payload["action"] = "insert";
+			payload["table"]  = "Logs";
+			payload["values"] = std::move(values);
+
+			const std::string resp = client.call(
+					json::serialize(payload), _TIMEOUT,
+					/*retry_on_refused=*/false);
+			auto obj = json::parse(resp).as_object();
+			if (!obj.at("success").as_bool()) {
+				std::string err = "unknown";
+				if (auto* ev = obj.if_contains("error")) {
+					if (ev->is_string()) err = ev->as_string().c_str();
+				}
+				std::cerr << "[LogC] INSERT 失败: " << err << std::endl;
+			}
+		}
+	} catch (const std::exception& e) {
+		// fail-safe：db 不可用时静默丢弃，绝不影响业务
+		std::cerr << "[LogC] 发送失败: " << e.what() << std::endl;
+	}
+}
+
+std::string LogC::_utc_now_iso() {
+	const auto now = std::chrono::system_clock::now();
+	const auto t   = std::chrono::system_clock::to_time_t(now);
+	const auto us  = std::chrono::duration_cast<std::chrono::microseconds>(
+			now.time_since_epoch()).count() % 1000000;
+	std::tm tm{};
+	::gmtime_r(&t, &tm);
+	char buf[40];
+	std::snprintf(buf, sizeof buf,
+			"%04d-%02d-%02dT%02d:%02d:%02d.%06d+00:00",
+			tm.tm_year + 1900, tm.tm_mon + 1, tm.tm_mday,
+			tm.tm_hour, tm.tm_min, tm.tm_sec, static_cast<int>(us));
+	return buf;
+}
+
+} // namespace qing