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/entity_spawn_callback_handler.hpp

@@ -0,0 +1,34 @@
+#pragma once
+
+#include <cstdint>
+#include <array>
+#include <functional>
+
+namespace wowee {
+
+namespace rendering { class Renderer; }
+namespace game { class GameHandler; }
+namespace core { class EntitySpawner; }
+
+namespace core {
+
+/// Handles entity spawn/despawn callbacks: creatures, players, game objects.
+class EntitySpawnCallbackHandler {
+public:
+    /// @param isLocalPlayerGuid Returns true if the given GUID is the local player (to skip self-spawn)
+    EntitySpawnCallbackHandler(EntitySpawner& entitySpawner,
+                               rendering::Renderer& renderer,
+                               game::GameHandler& gameHandler,
+                               std::function<bool(uint64_t)> isLocalPlayerGuid);
+
+    void setupCallbacks();
+
+private:
+    EntitySpawner& entitySpawner_;
+    rendering::Renderer& renderer_;
+    game::GameHandler& gameHandler_;
+    std::function<bool(uint64_t)> isLocalPlayerGuid_;
+};
+
+} // namespace core
+} // namespace wowee