Add metadata validation script and module documentation

- Introduced a new Python script `check_agents_metadata.py` for validating agent metadata, including YAML parsing, rating ranges, and cross-references.
- Added usage instructions and exit codes for the script.
- Created a new markdown file `模块目录和功能说明.md` to outline the directory structure and functionality of the modules.
- Added a text file `说明此文件不可AI修改.txt` to specify that certain files should not be modified by AI, including important information about the `dstalk` framework and its modules.

dstalk-core/src/boost_json.cpp

@@ -1 +1,7 @@
+/* @file boost_json.cpp
+ * @brief Boost.JSON header-only library compilation unit (single TU inclusion).
+ * Boost.JSON 仅头文件库的编译单元（单翻译单元包含）。
+ * Copyright (c) 2026 dstalk contributors. GPLv3.
+ */
+
 #include <boost/json/src.hpp>