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/src/net/http_client.hpp

@@ -0,0 +1,54 @@
+#pragma once
+
+#include <functional>
+#include <string>
+#include <unordered_map>
+
+namespace dstalk {
+namespace net {
+
+struct HttpResponse {
+    int status_code = 0;
+    std::string body;
+    std::unordered_map<std::string, std::string> headers;
+};
+
+/*
+ * HTTPS 客户端统一接口
+ * Windows: WinHTTP 实现 (零依赖)
+ * 其他平台: Boost.Beast + OpenSSL 实现
+ */
+class HttpClient {
+public:
+    HttpClient();
+    ~HttpClient();
+
+    void set_timeout(int connect_sec, int request_sec);
+
+    // 同步 POST JSON, 返回完整响应
+    HttpResponse post_json(
+        const std::string& host,
+        const std::string& port,
+        const std::string& target,
+        const std::string& json_body,
+        const std::unordered_map<std::string, std::string>& extra_headers
+    );
+
+    // 流式 POST (SSE 逐行回调), on_line 返回 false 提前终止
+    using StreamCallback = std::function<bool(const std::string& line)>;
+    HttpResponse post_stream(
+        const std::string& host,
+        const std::string& port,
+        const std::string& target,
+        const std::string& json_body,
+        const std::unordered_map<std::string, std::string>& extra_headers,
+        StreamCallback on_line
+    );
+
+private:
+    struct Impl;
+    Impl* impl_;
+};
+
+} // namespace net
+} // namespace dstalk