feat: implement OTA updates over HTTP(S), initiated over MQTT

components/mqtt_publisher/include/mqtt_publisher.h

@@ -13,6 +13,7 @@
 #define MQTT_DESELECTED_BIT           BIT4
 #define MQTT_FACTORY_RESET_BIT        BIT5
 #define MQTT_RECONFIGURE_SETTINGS_BIT BIT6
+#define MQTT_OTA_BIT                  BIT7
 
 /* Populated by handle_cmd() before MQTT_RECONFIGURE_SETTINGS_BIT is set.
  * All fields are optional — empty string means "not provided, leave unchanged". */
@@ -27,6 +28,18 @@ typedef struct {
  *  MQTT_RECONFIGURE_SETTINGS_BIT fires; must be read before the next MQTT event. */
 const mqtt_reconfigure_data_t *mqtt_publisher_get_reconfigure_data(void);
 
+typedef struct {
+    char url[256];
+    char version[32];
+} mqtt_ota_data_t;
+
+/** Returns a pointer to the last parsed OTA payload. Valid only after
+ *  MQTT_OTA_BIT fires; must be read before the next MQTT event. */
+const mqtt_ota_data_t *mqtt_publisher_get_ota_data(void);
+
+/** Publish OTA status to localiser/sensor/{id}/ota. Non-blocking (QoS 1). */
+void mqtt_publisher_send_ota_status(const char *status, const char *version);
+
 /**
  * Initialise and connect the MQTT client.
  *