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

include/audio/audio_coordinator.hpp

@@ -0,0 +1,66 @@
+#pragma once
+
+#include <memory>
+
+namespace wowee {
+namespace pipeline { class AssetManager; }
+namespace audio {
+
+class MusicManager;
+class FootstepManager;
+class ActivitySoundManager;
+class MountSoundManager;
+class NpcVoiceManager;
+class AmbientSoundManager;
+class UiSoundManager;
+class CombatSoundManager;
+class SpellSoundManager;
+class MovementSoundManager;
+
+/// Coordinates all audio subsystems.
+/// Extracted from Renderer to separate audio lifecycle from rendering.
+/// Owned by Application; Renderer and UI components access through Application.
+class AudioCoordinator {
+public:
+    AudioCoordinator();
+    ~AudioCoordinator();
+
+    /// Initialize the audio engine and all managers.
+    /// @return true if audio is available (engine initialized successfully)
+    bool initialize();
+
+    /// Initialize managers that need AssetManager (music lookups, sound banks).
+    void initializeWithAssets(pipeline::AssetManager* assetManager);
+
+    /// Shutdown all audio managers and engine.
+    void shutdown();
+
+    // Accessors for all audio managers (same interface as Renderer had)
+    MusicManager* getMusicManager() { return musicManager_.get(); }
+    FootstepManager* getFootstepManager() { return footstepManager_.get(); }
+    ActivitySoundManager* getActivitySoundManager() { return activitySoundManager_.get(); }
+    MountSoundManager* getMountSoundManager() { return mountSoundManager_.get(); }
+    NpcVoiceManager* getNpcVoiceManager() { return npcVoiceManager_.get(); }
+    AmbientSoundManager* getAmbientSoundManager() { return ambientSoundManager_.get(); }
+    UiSoundManager* getUiSoundManager() { return uiSoundManager_.get(); }
+    CombatSoundManager* getCombatSoundManager() { return combatSoundManager_.get(); }
+    SpellSoundManager* getSpellSoundManager() { return spellSoundManager_.get(); }
+    MovementSoundManager* getMovementSoundManager() { return movementSoundManager_.get(); }
+
+private:
+    std::unique_ptr<MusicManager> musicManager_;
+    std::unique_ptr<FootstepManager> footstepManager_;
+    std::unique_ptr<ActivitySoundManager> activitySoundManager_;
+    std::unique_ptr<MountSoundManager> mountSoundManager_;
+    std::unique_ptr<NpcVoiceManager> npcVoiceManager_;
+    std::unique_ptr<AmbientSoundManager> ambientSoundManager_;
+    std::unique_ptr<UiSoundManager> uiSoundManager_;
+    std::unique_ptr<CombatSoundManager> combatSoundManager_;
+    std::unique_ptr<SpellSoundManager> spellSoundManager_;
+    std::unique_ptr<MovementSoundManager> movementSoundManager_;
+
+    bool audioAvailable_ = false;
+};
+
+} // namespace audio
+} // namespace wowee