refactor: config (#30)

* refactor(config): replace singleton with dependency injection

* refactor(client_player): return ChunkPosSet by value in non-const getter

Copy the internal set under the mutex lock to avoid exposing a mutable reference that could be used unsafely after the lock is released. This fixes a potential data race when the caller holds the returned reference beyond the critical section. Also update the caller in `client_world` to remove the now-unnecessary `std::move`.

* fix(gameplay): prevent use-after-free in pending delete queues during destruction

* refactor(config): separate game and server configuration with explicit paths

src/CMakeLists.txt

@@ -10,7 +10,6 @@ target_sources(${PROJECT_NAME}
         gameplay/chunk_generator.cpp
         gameplay/tree.cpp
         input.cpp
-        map_table.cpp
         render/renderer.cpp
         shader.cpp
         texture_manager.cpp