refactor: enhance OTA update process with improved size checks and debugging output

src/ota.h

@@ -3,6 +3,12 @@
 
 #include <ESPAsyncWebServer.h>
 
+// Update size unknown constant, falls nicht bereits definiert
+#ifndef UPDATE_SIZE_UNKNOWN
+#define UPDATE_SIZE_UNKNOWN 0xFFFFFFFF
+#endif
+
+void stopAllTasks();
 void handleOTAUpload(AsyncWebServerRequest *request, String filename, size_t index, uint8_t *data, size_t len, bool final);
 
 #endif