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/ui_screen_callback_handler.hpp

@@ -0,0 +1,46 @@
+#pragma once
+
+#include <cstdint>
+#include <functional>
+#include <string>
+
+namespace wowee {
+
+namespace ui { class UIManager; }
+namespace game { class GameHandler; class ExpansionRegistry; }
+namespace auth { class AuthHandler; }
+namespace pipeline { class AssetManager; }
+
+namespace core {
+
+// Forward-declared in application.hpp
+enum class AppState;
+
+/// Handles authentication, realm selection, character selection/creation UI callbacks.
+/// Owns pendingCreatedCharacterName_.
+class UIScreenCallbackHandler {
+public:
+    using SetStateFn = std::function<void(AppState)>;
+
+    UIScreenCallbackHandler(ui::UIManager& uiManager,
+                            game::GameHandler& gameHandler,
+                            auth::AuthHandler& authHandler,
+                            game::ExpansionRegistry* expansionRegistry,
+                            pipeline::AssetManager* assetManager,
+                            SetStateFn setState);
+
+    void setupCallbacks();
+
+private:
+    ui::UIManager& uiManager_;
+    game::GameHandler& gameHandler_;
+    auth::AuthHandler& authHandler_;
+    game::ExpansionRegistry* expansionRegistry_;
+    pipeline::AssetManager* assetManager_;
+    SetStateFn setState_;
+
+    std::string pendingCreatedCharacterName_;  // Auto-select after character creation
+};
+
+} // namespace core
+} // namespace wowee