Fix web OTA upload and isolate OTA sessions across firmware and goTool.

Split ESP-NOW into core/master/slave modules, block non-OTA UART traffic during updates, and hold the host serial port exclusively so dashboard polling cannot interleave with firmware uploads.

Co-authored-by: Cursor <cursoragent@cursor.com>

main/ota_espnow.h

@@ -37,4 +37,10 @@ void ota_espnow_slave_on_end(const uint8_t master_mac[6]);
 void ota_espnow_progress_query(uint32_t filter_client_id,
                                alox_OtaSlaveProgressResponse *out);
 
+/** True while master is pushing a staged image to slaves. */
+bool ota_espnow_distribution_active(void);
+
+/** Slave: work queue for OTA (no esp_now_send from recv callback). */
+void ota_espnow_slave_init(void);
+
 #endif