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_session.h

@@ -0,0 +1,13 @@
+#ifndef OTA_SESSION_H
+#define OTA_SESSION_H
+
+#include <stdbool.h>
+#include <stdint.h>
+
+/** UART upload or ESP-NOW slave distribution in progress. */
+bool ota_session_busy(void);
+
+/** During OTA only UART OTA-related commands are accepted on the master. */
+bool ota_session_uart_cmd_allowed(uint16_t msg_id);
+
+#endif