Add cloud bridge and provisioning support for ESP32 gateway

- Introduced DaliCloudBridge for MQTT communication with backend.
- Added GatewayProvisioningStore for persisting cloud connection settings using NVS.
- Updated CMakeLists.txt to include new source files.
- Enhanced README.md with usage examples and configuration details.

include/gateway_cloud.hpp

@@ -0,0 +1,58 @@
+#pragma once
+
+#include "dali_comm.hpp"
+
+#include <atomic>
+#include <string>
+
+#ifdef ESP_PLATFORM
+#include "esp_event_base.h"
+#include "mqtt_client.h"
+#endif
+
+struct GatewayCloudConfig {
+  std::string brokerURI;
+  std::string deviceID;
+  std::string username = "device";
+  std::string password;
+  std::string topicPrefix = "devices";
+  int qos = 1;
+};
+
+// DaliCloudBridge bridges MQTT cloud topics and local DALI frames.
+class DaliCloudBridge {
+ public:
+  explicit DaliCloudBridge(DaliComm& comm);
+
+  bool start(const GatewayCloudConfig& config);
+  void stop();
+  bool isConnected() const;
+
+  bool publishStatus(const std::string& status);
+  bool publishRegister(const std::string& payloadJson);
+
+ private:
+#ifdef ESP_PLATFORM
+  static void mqttEventHandler(void* handler_args,
+                               esp_event_base_t base,
+                               int32_t event_id,
+                               void* event_data);
+  void onMqttEvent(esp_mqtt_event_handle_t event);
+#endif
+
+  bool handleDownlink(const std::string& payload);
+  bool publishJSON(const std::string& topic, const std::string& payloadJson);
+
+  std::string topicDown() const;
+  std::string topicUp() const;
+  std::string topicStatus() const;
+  std::string topicRegister() const;
+
+  DaliComm& comm_;
+  GatewayCloudConfig config_;
+  std::atomic<bool> connected_{false};
+
+#ifdef ESP_PLATFORM
+  esp_mqtt_client_handle_t client_ = nullptr;
+#endif
+};