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.

src/gateway_provisioning.cpp

@@ -0,0 +1,127 @@
+#include "gateway_provisioning.hpp"
+
+#ifdef ESP_PLATFORM
+extern "C" {
+#include "esp_log.h"
+#include "nvs.h"
+#include "nvs_flash.h"
+}
+
+namespace {
+constexpr const char* kTag = "gateway_provision";
+constexpr const char* kKeyBrokerURI = "broker_uri";
+constexpr const char* kKeyDeviceID = "device_id";
+constexpr const char* kKeyUsername = "username";
+constexpr const char* kKeyPassword = "password";
+constexpr const char* kKeyTopicPrefix = "topic_prefix";
+constexpr const char* kKeyQos = "qos";
+
+esp_err_t writeString(nvs_handle_t handle, const char* key, const std::string& value) {
+  return nvs_set_str(handle, key, value.c_str());
+}
+
+esp_err_t readString(nvs_handle_t handle, const char* key, std::string* value) {
+  size_t required = 0;
+  esp_err_t err = nvs_get_str(handle, key, nullptr, &required);
+  if (err != ESP_OK) {
+    return err;
+  }
+  std::string buf(required, '\0');
+  err = nvs_get_str(handle, key, buf.data(), &required);
+  if (err != ESP_OK) {
+    return err;
+  }
+  if (!buf.empty() && buf.back() == '\0') {
+    buf.pop_back();
+  }
+  *value = buf;
+  return ESP_OK;
+}
+}  // namespace
+
+esp_err_t GatewayProvisioningStore::save(const GatewayCloudConfig& config) const {
+  nvs_handle_t handle;
+  esp_err_t err = nvs_open(nvsNamespace_.c_str(), NVS_READWRITE, &handle);
+  if (err != ESP_OK) {
+    ESP_LOGE(kTag, "nvs_open(save) failed: %s", esp_err_to_name(err));
+    return err;
+  }
+
+  err = writeString(handle, kKeyBrokerURI, config.brokerURI);
+  if (err == ESP_OK) err = writeString(handle, kKeyDeviceID, config.deviceID);
+  if (err == ESP_OK) err = writeString(handle, kKeyUsername, config.username);
+  if (err == ESP_OK) err = writeString(handle, kKeyPassword, config.password);
+  if (err == ESP_OK) err = writeString(handle, kKeyTopicPrefix, config.topicPrefix);
+  if (err == ESP_OK) err = nvs_set_i32(handle, kKeyQos, config.qos);
+  if (err == ESP_OK) err = nvs_commit(handle);
+
+  nvs_close(handle);
+  if (err != ESP_OK) {
+    ESP_LOGE(kTag, "save failed: %s", esp_err_to_name(err));
+  }
+  return err;
+}
+
+esp_err_t GatewayProvisioningStore::load(GatewayCloudConfig* config) const {
+  if (config == nullptr) {
+    return ESP_ERR_INVALID_ARG;
+  }
+
+  nvs_handle_t handle;
+  esp_err_t err = nvs_open(nvsNamespace_.c_str(), NVS_READONLY, &handle);
+  if (err != ESP_OK) {
+    return err;
+  }
+
+  err = readString(handle, kKeyBrokerURI, &config->brokerURI);
+  if (err == ESP_OK) err = readString(handle, kKeyDeviceID, &config->deviceID);
+  if (err == ESP_OK) err = readString(handle, kKeyUsername, &config->username);
+  if (err == ESP_OK) err = readString(handle, kKeyPassword, &config->password);
+
+  esp_err_t topicErr = readString(handle, kKeyTopicPrefix, &config->topicPrefix);
+  if (topicErr != ESP_OK) {
+    config->topicPrefix = "devices";
+  }
+
+  int32_t qos = 1;
+  esp_err_t qosErr = nvs_get_i32(handle, kKeyQos, &qos);
+  if (qosErr == ESP_OK) {
+    config->qos = qos;
+  } else {
+    config->qos = 1;
+  }
+
+  nvs_close(handle);
+  return err;
+}
+
+esp_err_t GatewayProvisioningStore::clear() const {
+  nvs_handle_t handle;
+  esp_err_t err = nvs_open(nvsNamespace_.c_str(), NVS_READWRITE, &handle);
+  if (err != ESP_OK) {
+    return err;
+  }
+
+  err = nvs_erase_all(handle);
+  if (err == ESP_OK) {
+    err = nvs_commit(handle);
+  }
+  nvs_close(handle);
+  return err;
+}
+
+#else
+
+esp_err_t GatewayProvisioningStore::save(const GatewayCloudConfig& config) const {
+  (void)config;
+  return -1;
+}
+
+esp_err_t GatewayProvisioningStore::load(GatewayCloudConfig* config) const {
+  (void)config;
+  return -1;
+}
+
+esp_err_t GatewayProvisioningStore::clear() const { return -1; }
+
+#endif