extract loadModules into ConfigLoaderModules.cpp

Continues the ConfigLoader.cpp domain split. StatEntry/kKnownStats are
only used by loadModules, so they move along as a domain-local
anonymous-namespace table rather than into TomlHelpers. Pure move; no
logic change.

Co-Authored-By: Claude <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01YHcUerKAZKWNvSKJxYKbnG

src/lib/config/CMakeLists.txt

@@ -26,6 +26,7 @@ SET(SRCS
     ${CMAKE_CURRENT_SOURCE_DIR}/ConfigLoaderRecipes.cpp
     ${CMAKE_CURRENT_SOURCE_DIR}/ConfigLoaderShips.cpp
     ${CMAKE_CURRENT_SOURCE_DIR}/ConfigLoaderStations.cpp
+    ${CMAKE_CURRENT_SOURCE_DIR}/ConfigLoaderModules.cpp
     ${CMAKE_CURRENT_SOURCE_DIR}/SurfaceMask.cpp
     ${CMAKE_CURRENT_SOURCE_DIR}/BlueprintSerializer.cpp
     ${CMAKE_CURRENT_SOURCE_DIR}/ShipLayoutBlueprintSerializer.cpp