Initial dstalk project: core DLL + CLI + BearSSL TLS

- Core DLL: AI API client (DeepSeek/OpenAI compatible), HTTP(S) via Boost.Beast
- BearSSL vendored as TLS backend (MIT license, replacing OpenSSL)
- CLI frontend with ANSI colors, /help /model /file /save /load commands
- WinHTTP alternative HTTP client for Windows
- GPLv3 license with linking exception
- Build: CMake + Ninja + Clang, dependencies via Conan2

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

dstalk-core/include/dstalk/dstalk_api.h

@@ -0,0 +1,52 @@
+#ifndef DSTALK_API_H
+#define DSTALK_API_H
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+/* ---- DLL 导出 / 导入宏 ---- */
+#if defined(_WIN32)
+    #ifdef DSTALK_BUILD_DLL
+        #define DSTALK_API __declspec(dllexport)
+    #else
+        #define DSTALK_API __declspec(dllimport)
+    #endif
+#else
+    #define DSTALK_API __attribute__((visibility("default")))
+#endif
+
+/* ---- 初始化和配置 ---- */
+DSTALK_API int  dstalk_init(const char* config_path);
+DSTALK_API void dstalk_destroy(void);
+
+/* 在 init 之后可修改 API 参数 (init 也会从配置文件读取) */
+DSTALK_API void dstalk_set_api_key(const char* api_key);
+DSTALK_API void dstalk_set_base_url(const char* base_url);
+DSTALK_API void dstalk_set_model(const char* model);
+
+/* ---- AI 对话 ---- */
+/* 同步对话: 发送 input，返回完整 AI 回复 (调用方通过 dstalk_free_string 释放) */
+DSTALK_API int  dstalk_chat(const char* input, char** output);
+
+/* 流式对话: 每收到一个 token 调用回调，回调返回 0 可提前取消 */
+typedef int (*dstalk_stream_cb)(const char* token, void* userdata);
+DSTALK_API int  dstalk_chat_stream(const char* input, dstalk_stream_cb cb, void* userdata);
+
+/* 释放由 dstalk_chat / dstalk_file_read 分配的字符串 */
+DSTALK_API void dstalk_free_string(char* str);
+
+/* ---- 会话管理 ---- */
+DSTALK_API void dstalk_session_clear(void);   /* 清空对话历史 */
+DSTALK_API int  dstalk_session_save(const char* path);  /* 保存会话到文件 */
+DSTALK_API int  dstalk_session_load(const char* path);  /* 从文件恢复会话 */
+
+/* ---- 文件操作 ---- */
+DSTALK_API int  dstalk_file_read(const char* path, char** content);
+DSTALK_API int  dstalk_file_write(const char* path, const char* content);
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif /* DSTALK_API_H */