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-gui/CMakeLists.txt

@@ -0,0 +1,15 @@
+# ============================================================
+# dstalk-gui — 图形化前端 (SDL3)
+# ============================================================
+
+find_package(SDL3 REQUIRED)
+
+add_executable(dstalk-gui
+    src/main.cpp
+)
+
+target_link_libraries(dstalk-gui
+    PRIVATE
+        dstalk
+        SDL3::SDL3
+)