Integrate Paho MQTT C library into project. Updated CMakeLists.txt to find PahoMqttC package and added fallback for manual linking. Refactored mqtt.hpp and mqtt.cpp to utilize Paho MQTT C API, replacing previous async client implementation. Added Windows setup guide for MQTT library installation.

MQTT_SETUP_WINDOWS.md

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+# Windows MQTT库安装指南
+
+## 方法1: 使用vcpkg (推荐)
+
+### 1. 安装vcpkg
+```cmd
+git clone https://github.com/Microsoft/vcpkg.git
+cd vcpkg
+.\bootstrap-vcpkg.bat
+```
+
+### 2. 安装MQTT库
+```cmd
+.\vcpkg install paho-mqtt:x64-windows
+.\vcpkg install paho-mqttpp3:x64-windows
+.\vcpkg install nlohmann-json:x64-windows
+```
+
+### 3. 集成到CMake
+```cmd
+.\vcpkg integrate install
+```
+
+### 4. 修改CMake命令
+在构建时添加vcpkg工具链：
+```cmd
+mkdir build
+cd build
+cmake .. -DCMAKE_TOOLCHAIN_FILE=[vcpkg根目录]/scripts/buildsystems/vcpkg.cmake
+cmake --build .
+```
+
+## 方法2: 手动编译
+
+### 1. 编译Paho MQTT C库
+```cmd
+git clone https://github.com/eclipse/paho.mqtt.c.git
+cd paho.mqtt.c
+mkdir build
+cd build
+cmake .. -DPAHO_BUILD_STATIC=TRUE -DPAHO_BUILD_SHARED=FALSE
+cmake --build . --config Release
+cmake --install . --prefix C:/mqtt/c
+```
+
+### 2. 编译Paho MQTT C++库
+```cmd
+git clone https://github.com/eclipse/paho.mqtt.cpp.git
+cd paho.mqtt.cpp
+mkdir build
+cd build
+cmake .. -DPAHO_MQTT_C_PATH=C:/mqtt/c -DPAHO_BUILD_STATIC=TRUE
+cmake --build . --config Release
+cmake --install . --prefix C:/mqtt/cpp
+```
+
+### 3. 修改CMakeLists.txt
+添加库路径：
+```cmake
+set(CMAKE_PREFIX_PATH "C:/mqtt/cpp;C:/mqtt/c")
+find_package(PahoMqttCpp REQUIRED)
+```
+
+## 验证安装
+
+运行以下命令验证：
+```cmd
+cd build
+cmake ..
+```
+
+如果没有错误，说明MQTT库已正确配置。
+
+## 使用示例
+
+在您的代码中导入MQTT：
+```cpp
+#include <mqtt/async_client.h>
+#include "mqtt.hpp"
+
+// 创建MQTT客户端
+auto mqttClient = std::make_unique<custom::MqttClient>("localhost", 1883, "test_client");
+mqttClient->connect();
+mqttClient->subscribe("test/topic");
+```