Fix macOS build: drop Boost::system/find_package component, use std::filesystem

Homebrew's boost formula doesn't ship the boost_system CMake config file,
so find_package(Boost REQUIRED COMPONENTS system) failed on macOS.

- Replace boost::filesystem with std::filesystem (C++17, no Boost dep)
- Drop 'filesystem' from find_package — only headers needed (asio + system)
- Link libboost_system explicitly per-platform by library name, resolved
  via the platform's default search path (Homebrew toolchain on macOS,
  system libs on Linux, MSYS2 on Windows)

CI will rerun automatically on PR push.

src/CMakeLists.txt

@@ -258,14 +258,20 @@ if(BUILD_CLI)
     add_executable(triangles-cli
         triangles-cli.cpp
     )
-    # Boost components used by the CLI
-    find_package(Boost REQUIRED COMPONENTS filesystem system)
+    # Boost: only need headers for asio + system. Boost::system gets resolved at
+    # link time via the platform's default library search path (libboost_system
+    # on Linux, libboost_system.dylib on macOS Homebrew, libboost_system-mt-*.dll
+    # on Windows MSYS2). Avoids needing a per-component CMake config file.
+    find_package(Boost REQUIRED)
     target_link_libraries(triangles-cli
         PRIVATE
             json_compat
-            Boost::filesystem
-            Boost::system
     )
+    if(UNIX AND NOT APPLE)
+        # Linux: explicit link to libboost_system (header-only Boost.System
+        # is rare; we explicitly link the small compiled library).
+        target_link_libraries(triangles-cli PRIVATE boost_system)
+    endif()
 
     if(WIN32)
         set_target_properties(triangles-cli PROPERTIES SUFFIX ".exe")
@@ -273,6 +279,13 @@ if(BUILD_CLI)
         target_link_libraries(triangles-cli PRIVATE ws2_32)
     endif()
 
+    if(APPLE)
+        # macOS Homebrew ships libboost_system.dylib without a CMake config
+        # file, so link by library name (resolved via Homebrew's compiler
+        # toolchain search paths).
+        target_link_libraries(triangles-cli PRIVATE boost_system)
+    endif()
+
     if(MSVC)
         set_target_properties(triangles-cli PROPERTIES
             VS_WINRT_COMPONENT "console"

src/triangles-cli.cpp

@@ -41,8 +41,7 @@
 #include <boost/asio.hpp>
 #include <boost/asio/streambuf.hpp>
 
-#include <boost/filesystem/operations.hpp>
-#include <boost/filesystem/path.hpp>
+#include <filesystem>
 
 #include <algorithm>
 #include <cstdint>
@@ -62,7 +61,7 @@
 using namespace std;
 namespace asio = boost::asio;
 using boost::asio::ip::tcp;
-namespace fs = boost::filesystem;
+namespace fs = std::filesystem;
 using namespace json_spirit;
 
 // ─────────────────────────────────────────────────────────────────────────────