cmake: add WITH_CGAL / WITH_VIEWER modes, remove unused Boost

Restructures the CMake build into three clearly separated modes:

  (default)        tests only – Eigen + GTest, no heavy deps
  -DWITH_VIEWER=ON builds viewer lib (libigl / GLFW / GLAD)
  -DWITH_CGAL=ON   builds conformallab_core CLI app;
                   implies WITH_VIEWER automatically

Changes:
- code/CMakeLists.txt: viewer and core targets are now guarded by
  option() flags; GTest / tests target is always built
- code/deps/Cmakelists.txt: CGAL, libigl, glfw, glad are only
  extracted when the corresponding mode is enabled; Eigen always
- Remove Boost (211 MB tarball, 0 usages in the codebase – CGAL 6.x
  does not require Boost for Simple_cartesian / Surface_mesh / basic IO)
- Remove code/src/main.cpp (dead file, not referenced in CMake)

All 16 C++ tests pass in tests-only mode (verified locally).

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

code/CMakeLists.txt

@@ -1,13 +1,31 @@
 cmake_minimum_required(VERSION 3.20)
-# Automatisch Projektname aus Parent-Ordner
 
 set(PROJECT_NAME "conformallab_core")
-
 project(${PROJECT_NAME} LANGUAGES C CXX)
 
 message(STATUS "Configuring ${PROJECT_NAME}...")
 
-# Build-Setup
+# ── Build modes ────────────────────────────────────────────────────────────────
+#
+#   Default (CI / tests-only): only Eigen + GTest are required.
+#
+#   -DWITH_CGAL=ON   builds the conformallab_core CLI app (needs CGAL).
+#                    Automatically enables WITH_VIEWER because the app uses
+#                    the viewer library for mesh visualisation.
+#
+#   -DWITH_VIEWER=ON builds the viewer library standalone (libigl/GLFW/GLAD).
+#
+# ──────────────────────────────────────────────────────────────────────────────
+option(WITH_CGAL   "Build conformallab_core app (requires CGAL + Viewer)" OFF)
+option(WITH_VIEWER "Build viewer library (libigl / GLFW / GLAD)"          OFF)
+
+# The CLI app always needs the viewer; enable it implicitly.
+if(WITH_CGAL AND NOT WITH_VIEWER)
+    message(STATUS "WITH_CGAL implies WITH_VIEWER – enabling automatically.")
+    set(WITH_VIEWER ON CACHE BOOL "" FORCE)
+endif()
+
+# ── Standard settings ──────────────────────────────────────────────────────────
 set(CMAKE_CXX_STANDARD 17)
 set(CMAKE_CXX_STANDARD_REQUIRED ON)
 set(CMAKE_CXX_EXTENSIONS OFF)
@@ -18,20 +36,18 @@ if(NOT CMAKE_BUILD_TYPE)
   set(CMAKE_BUILD_TYPE "Release" CACHE STRING "Build type" FORCE)
 endif()
 
-# Compiler-Warnings & Optimierungen
 if(CMAKE_CXX_COMPILER_ID MATCHES "Clang|GNU")
   add_compile_options(-Wall -Wextra -Wpedantic)
-  
-  # AddressSanitizer nur im Debug (nicht für Tests, da gtest_discover_tests
-  # die Binary zur Buildzeit ausführt und ASan dabei hängt)
+
+  # AddressSanitizer only in Debug (gtest_discover_tests runs the binary at
+  # configure time and hangs with ASan enabled).
   if(CMAKE_BUILD_TYPE STREQUAL "Debug" AND NOT BUILD_TESTING)
     add_compile_options(-fsanitize=address -fno-omit-frame-pointer)
     add_link_options(-fsanitize=address)
   endif()
 endif()
 
-
-# ----- Testing (Google Test via FetchContent) -----
+# ── GTest (always – tests are always built) ────────────────────────────────────
 include(FetchContent)
 include(CTest)
 enable_testing()
@@ -45,38 +61,44 @@ set(gtest_force_shared_crt ON CACHE BOOL "" FORCE)
 set(INSTALL_GTEST          OFF CACHE BOOL "" FORCE)
 set(BUILD_GMOCK            OFF CACHE BOOL "" FORCE)
 FetchContent_MakeAvailable(googletest)
-# --------------------------------------------------
 
+# ── External deps (lazy tarball extraction) ────────────────────────────────────
 add_subdirectory(deps)
-add_subdirectory(deps/glfw-3.4)
 
-# --------- GLAD (global) ---------
-add_library(glad STATIC ${CMAKE_CURRENT_SOURCE_DIR}/deps/libigl-glad/src/glad.c)
-target_include_directories(glad PUBLIC ${CMAKE_CURRENT_SOURCE_DIR}/deps/libigl-glad/include)
-# --------- VIEWER Lib (separat → nur bei src/viewer/* Änderung gebaut!) ---------
-add_library(viewer STATIC src/viewer/simple_viewer.cpp)
-target_include_directories(viewer PUBLIC
-  ${CMAKE_CURRENT_SOURCE_DIR}/deps/libigl-2.6.0/include
-  ${CMAKE_CURRENT_SOURCE_DIR}/include  
-  ${CMAKE_CURRENT_SOURCE_DIR}/deps/libigl-glad/include
-  ${CMAKE_CURRENT_SOURCE_DIR}/deps/eigen-3.4.0/
-)  
-target_link_libraries(viewer PUBLIC glad glfw)  
-# --------- Executable ---------
-add_executable(${PROJECT_NAME} src/apps/v0/conformallab_cli.cpp)
-target_include_directories(${PROJECT_NAME} SYSTEM PRIVATE
-  ${CMAKE_CURRENT_SOURCE_DIR}/deps/single_includes
-  ${CMAKE_CURRENT_SOURCE_DIR}/deps/eigen-3.4.0/
-  ${CMAKE_CURRENT_SOURCE_DIR}/deps/CGAL-6.1.1/include
-  ${CMAKE_CURRENT_SOURCE_DIR}/deps/boost_1_90_0/
-  ${CMAKE_CURRENT_SOURCE_DIR}/deps/libigl-2.6.0/include  
-)
-target_include_directories(${PROJECT_NAME} PRIVATE ${CMAKE_CURRENT_SOURCE_DIR}/include)
-#-------- Compiler-Definitionen ---------
-target_compile_definitions(${PROJECT_NAME} PRIVATE CGAL_DISABLE_GMP CGAL_DISABLE_MPFR)
-target_link_libraries(${PROJECT_NAME} PRIVATE viewer)
-#--------- Output-Ordner ---------
-set_target_properties(${PROJECT_NAME} PROPERTIES RUNTIME_OUTPUT_DIRECTORY ${CMAKE_CURRENT_SOURCE_DIR}/bin)
+# ── Viewer library (optional) ──────────────────────────────────────────────────
+if(WITH_VIEWER)
+    add_subdirectory(deps/glfw-3.4)
 
+    add_library(glad STATIC
+        ${CMAKE_CURRENT_SOURCE_DIR}/deps/libigl-glad/src/glad.c)
+    target_include_directories(glad PUBLIC
+        ${CMAKE_CURRENT_SOURCE_DIR}/deps/libigl-glad/include)
+
+    add_library(viewer STATIC src/viewer/simple_viewer.cpp)
+    target_include_directories(viewer PUBLIC
+        ${CMAKE_CURRENT_SOURCE_DIR}/deps/libigl-2.6.0/include
+        ${CMAKE_CURRENT_SOURCE_DIR}/include
+        ${CMAKE_CURRENT_SOURCE_DIR}/deps/libigl-glad/include
+        ${CMAKE_CURRENT_SOURCE_DIR}/deps/eigen-3.4.0/)
+    target_link_libraries(viewer PUBLIC glad glfw)
+endif()
+
+# ── Core CLI app (optional, requires CGAL + Viewer) ───────────────────────────
+if(WITH_CGAL)
+    add_executable(${PROJECT_NAME} src/apps/v0/conformallab_cli.cpp)
+    target_include_directories(${PROJECT_NAME} SYSTEM PRIVATE
+        ${CMAKE_CURRENT_SOURCE_DIR}/deps/single_includes
+        ${CMAKE_CURRENT_SOURCE_DIR}/deps/eigen-3.4.0/
+        ${CMAKE_CURRENT_SOURCE_DIR}/deps/CGAL-6.1.1/include
+        ${CMAKE_CURRENT_SOURCE_DIR}/deps/libigl-2.6.0/include)
+    target_include_directories(${PROJECT_NAME} PRIVATE
+        ${CMAKE_CURRENT_SOURCE_DIR}/include)
+    target_compile_definitions(${PROJECT_NAME} PRIVATE
+        CGAL_DISABLE_GMP CGAL_DISABLE_MPFR)
+    target_link_libraries(${PROJECT_NAME} PRIVATE viewer)
+    set_target_properties(${PROJECT_NAME} PROPERTIES
+        RUNTIME_OUTPUT_DIRECTORY ${CMAKE_CURRENT_SOURCE_DIR}/bin)
+endif()
+
+# ── Tests (always) ────────────────────────────────────────────────────────────
 add_subdirectory(tests)
-