User folders: save games and Settings.cfg in Documents\Sacred

The game's ANSI file API calls are hooked; paths under save\ and
Settings.cfg are redirected to Documents\Sacred\save and
Documents\Sacred\config, copied there once from the game folder.
The shared chest uses the same save folder.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

CMakeLists.txt

@@ -70,6 +70,7 @@ add_library(sacredK SHARED
     src/mods/charexport.cpp
     src/mods/options.cpp
     src/mods/lootfilter.cpp
+    src/mods/userfolders.cpp
 )
 target_include_directories(sacredK PRIVATE src)
 target_compile_options(sacredK PRIVATE ${SACREDK_CXX_FLAGS})