Implement NPC greeting voice lines

Added NPC voice manager that plays greeting sounds when clicking on NPCs:

Features:
- Voice line library with multiple race/gender voice types (Human, Dwarf,
  Night Elf, etc.)
- 3D positional audio - voice comes from NPC location
- Cooldown system prevents spam clicking same NPC
- Randomized pitch/volume for variety
- Loads greeting sounds from character voice files in MPQ
- Generic fallback voices for NPCs without specific voice types

Voice lines trigger automatically when gossip window opens (SMSG_GOSSIP_MESSAGE).
Uses same audio system as other sound effects with ma_sound_set_position.

src/core/application.cpp

@@ -6,6 +6,7 @@
 #include "core/logger.hpp"
 #include "core/memory_monitor.hpp"
 #include "rendering/renderer.hpp"
+#include "audio/npc_voice_manager.hpp"
 #include "rendering/camera.hpp"
 #include "rendering/camera_controller.hpp"
 #include "rendering/terrain_renderer.hpp"
@@ -814,6 +815,15 @@ void Application::setupUICallbacks() {
         }
     });
 
+    // NPC greeting callback - play voice line
+    gameHandler->setNpcGreetingCallback([this](uint64_t guid, const glm::vec3& position) {
+        if (renderer && renderer->getNpcVoiceManager()) {
+            // Convert canonical to render coords for 3D audio
+            glm::vec3 renderPos = core::coords::canonicalToRender(position);
+            renderer->getNpcVoiceManager()->playGreeting(guid, audio::VoiceType::GENERIC, renderPos);
+        }
+    });
+
     // "Create Character" button on character screen
     uiManager->getCharacterScreen().setOnCreateCharacter([this]() {
         uiManager->getCharacterCreateScreen().reset();