refactor: decouple Application singleton by extracting core subsystems and updating interfaces

- Add `audio::AudioCoordinator` interface and implementation
- Modify `Application` to reduce singleton usage and move controller responsibilities:
  - application.hpp
  - application.cpp
- Update UI and audio headers/sources:
  - game_screen.hpp
  - game_screen.cpp
  - ui_manager.hpp
  - audio_coordinator.hpp
  - audio_coordinator.cpp
- Project config touched:
  - CMakeLists.txt

src/core/application.cpp

@@ -31,6 +31,7 @@
 #include "audio/footstep_manager.hpp"
 #include "audio/activity_sound_manager.hpp"
 #include "audio/audio_engine.hpp"
+#include "audio/audio_coordinator.hpp"
 #include "addons/addon_manager.hpp"
 #include <imgui.h>
 #include "pipeline/m2_loader.hpp"
@@ -223,6 +224,11 @@ bool Application::initialize() {
             renderer.get(), assetManager.get(), gameHandler.get(),
             dbcLayout_.get(), entitySpawner_.get());
 
+        // Wire AppearanceComposer to UI components (Phase A singleton breaking)
+        if (uiManager) {
+            uiManager->setAppearanceComposer(appearanceComposer_.get());
+        }
+
         // Ensure the main in-world CharacterRenderer can load textures immediately.
         // Previously this was only wired during terrain initialization, which meant early spawns
         // (before terrain load) would render with white fallback textures (notably hair).