refactor(core): decompose Application::setupUICallbacks() into 7 domain handlers

Extract ~1,700 lines / 60+ inline [this]-capturing lambdas from the monolithic
Application::setupUICallbacks() into 7 focused callback handler classes following
the ToastManager/ChatPanel::setupCallbacks() pattern already in the codebase.

New handlers (include/core/ + src/core/):
  - NPCInteractionCallbackHandler  NPC greeting/farewell/vendor/aggro voice
  - AudioCallbackHandler           Music, positional sound, level-up, achievement, LFG
  - EntitySpawnCallbackHandler     Creature/player/GO spawn, despawn, move, state
  - AnimationCallbackHandler       Death, respawn, combat, emotes, charge, sprint, vehicle
  - TransportCallbackHandler       Mount, taxi, transport spawn/move
  - WorldEntryCallbackHandler      World entry, unstuck, hearthstone, bind point
  - UIScreenCallbackHandler        Auth, realm selection, char selection/creation/deletion

application.cpp:  4,462 → 2,791 lines  (−1,671)
setupUICallbacks: ~1,700 → ~50 lines (thin orchestrator)

Deduplication:
  resolveSoundEntryPath()   — was 3× copy-paste of SoundEntries.dbc lookup
  resolveNpcVoiceType()     — was 4× copy-paste of display-ID→voice detection
  precacheNearbyTiles()     — was 3× copy-paste of 17×17 tile loop
  4 helper lambdas          — promoted to private methods on WorldEntryCallbackHandler

State migration out of Application:
  charge* (6 vars)          → AnimationCallbackHandler
  hearth*/worldEntry*/taxi* → WorldEntryCallbackHandler
  pendingCreatedCharacterName_ → UIScreenCallbackHandler

Bug fixes:
  - Duplicate `namespace core {` in application.hpp caused wowee::std pollution
  - AppState forward decl in ui_screen_callback_handler.hpp was at wrong scope
  - world_loader.cpp accessed moved member vars directly via friend; now uses handler API

include/core/audio_callback_handler.hpp

@@ -0,0 +1,40 @@
+#pragma once
+
+#include <cstdint>
+#include <string>
+#include <optional>
+
+namespace wowee {
+
+namespace rendering { class Renderer; }
+namespace game { class GameHandler; }
+namespace audio { class AudioCoordinator; }
+namespace pipeline { class AssetManager; }
+namespace ui { class UIManager; }
+
+namespace core {
+
+/// Handles audio-related callbacks: music, sound effects, level-up, achievement, LFG.
+class AudioCallbackHandler {
+public:
+    AudioCallbackHandler(pipeline::AssetManager& assetManager,
+                         audio::AudioCoordinator* audioCoordinator,
+                         rendering::Renderer* renderer,
+                         ui::UIManager* uiManager,
+                         game::GameHandler& gameHandler);
+
+    void setupCallbacks();
+
+private:
+    /// Resolve SoundEntries.dbc → file path for a given soundId (eliminates 3x copy-paste)
+    std::optional<std::string> resolveSoundEntryPath(uint32_t soundId) const;
+
+    pipeline::AssetManager& assetManager_;
+    audio::AudioCoordinator* audioCoordinator_;
+    rendering::Renderer* renderer_;
+    ui::UIManager* uiManager_;
+    game::GameHandler& gameHandler_;
+};
+
+} // namespace core
+} // namespace wowee