docs: update file inventory and module header contracts

Refresh both AGENTS guides and clarify module purpose, usage, ownership, threading, return values and wire formats in headers. Remove the unused timeout_heap freed_count field and unimplemented getter.

tools/chatgui/src/qrcode_utils.h

@@ -1,3 +1,4 @@
+/* Генерация QR и распознавание штрихкодов из QImage через ZXingQt. Ошибка генерации — пустой QImage. */
 #pragma once
 
 #include <QImage>