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>

tools/env.bat

@@ -0,0 +1,13 @@
+@echo off
+:: ============================================================
+:: env.bat — 将 tools\ 内工具加入 PATH
+:: ============================================================
+
+set "TOOLS=%~dp0"
+
+if exist "%TOOLS%cmake\bin"    set "PATH=%TOOLS%cmake\bin;%PATH%"
+if exist "%TOOLS%ninja"        set "PATH=%TOOLS%ninja;%PATH%"
+if exist "%TOOLS%llvm\bin"     set "PATH=%TOOLS%llvm\bin;%PATH%"
+if exist "%TOOLS%conan2"       set "PATH=%TOOLS%conan2;%PATH%"
+
+echo [dstalk] tools\ 工具链已加载