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_provisioning.hpp

@@ -0,0 +1,27 @@
+#pragma once
+
+#include "gateway_cloud.hpp"
+
+#include <string>
+
+#ifdef ESP_PLATFORM
+extern "C" {
+#include "esp_err.h"
+}
+#else
+using esp_err_t = int;
+#endif
+
+// Stores/loads gateway cloud configuration using ESP-IDF NVS.
+class GatewayProvisioningStore {
+ public:
+  explicit GatewayProvisioningStore(std::string nvsNamespace = "dali_cloud")
+      : nvsNamespace_(std::move(nvsNamespace)) {}
+
+  esp_err_t save(const GatewayCloudConfig& config) const;
+  esp_err_t load(GatewayCloudConfig* config) const;
+  esp_err_t clear() const;
+
+ private:
+  std::string nvsNamespace_;
+};