build: modernize repo-lens skeleton and cross-platform configuration

Replace CPM with FetchContent and update GoogleTest to v1.18.0.
Add compiler toolchains and Debug, Release, and sanitizer presets.
Require CMake 4.0, use target properties for compiler settings,
and enable compilation database export.

Fix skeleton compilation errors and adopt trailing return types,
nodiscard execute methods, and noexcept signatures. Update CI
and project documentation without implementing any TODOs.

Validated Windows builds and tests in all three configurations.

CMakeLists.txt

@@ -1,25 +1,27 @@
-cmake_minimum_required(VERSION 3.23)
+cmake_minimum_required(VERSION 4.0)
 
-project(blank-slate VERSION 1.0.0)
+project(repo-lens VERSION 1.0.0 LANGUAGES CXX)
 
 set(CMAKE_CXX_STANDARD 20)
 set(CMAKE_CXX_STANDARD_REQUIRED true)
-set(CMAKE_CONFIGURATION_TYPES "Debug;Release" CACHE STRING "" FORCE)
+set(CMAKE_CXX_EXTENSIONS OFF)
+set(CMAKE_EXPORT_COMPILE_COMMANDS ON CACHE BOOL "Generate compile_commands.json with supported generators")
 
 set_property(GLOBAL PROPERTY USE_FOLDERS ON)
 OPTION(ENABLE_TESTS "Enable Unit Tests" ON)
 OPTION(ENABLE_ALL_REASONABLE_WARNINGS "Enable all possible reasonable warnings" ON )
 OPTION(ENABLE_WARNINGS_AS_ERRORS "Warnings are treated as Errors" ON)
 OPTION(ENABLE_STATIC_ANALYSIS "Enable Static Analysis Tools" ON)
-OPTION(ENABLE_SANITIZERS "Enable Sanitizer Tools" ON)
+OPTION(ENABLE_SANITIZERS "Enable Sanitizer Tools" OFF)
 
 list(APPEND CMAKE_MODULE_PATH ${CMAKE_CURRENT_SOURCE_DIR}/cmake)
 
 include(compilerwarnings)
 include(sanitizers)
 include(staticanalysis)
-include(cpm)
 
+# @ai-bookmark OPTIONAL_TEST_DEPENDENCY_BOUNDARY
+# Keep dependency downloads inside the optional test path; the application builds offline.
 if (ENABLE_TESTS)
     message("-- Unit Testing Enabled")
     enable_testing()