Add unit tests for OpenAI plugin and establish coding standards

- Introduced comprehensive unit tests for the OpenAI plugin, covering SSE parsing, sentinel matching, delta extraction, request building, and more.
- Created a new markdown file detailing coding and naming conventions for the dstalk project, including guidelines for comments, naming rules, code organization, and memory management practices.

plugins/openai/CMakeLists.txt

@@ -0,0 +1,20 @@
+# ============================================================
+# plugin-openai — OpenAI 兼容 AI 服务 / OpenAI-compatible AI service
+# ============================================================
+
+find_package(Boost REQUIRED CONFIG)
+
+add_library(plugin-openai SHARED
+    src/openai_plugin.cpp
+)
+
+target_link_libraries(plugin-openai PRIVATE dstalk)
+
+# Boost.JSON (header-only)
+find_package(Boost REQUIRED CONFIG)
+target_link_libraries(plugin-openai PRIVATE boost::boost dstalk_boost_config)
+
+set_target_properties(plugin-openai PROPERTIES
+    LIBRARY_OUTPUT_DIRECTORY ${CMAKE_BINARY_DIR}/plugins
+    RUNTIME_OUTPUT_DIRECTORY ${CMAKE_BINARY_DIR}/plugins
+)