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/rendering/renderer.cpp

@@ -37,6 +37,7 @@
 #include "audio/footstep_manager.hpp"
 #include "audio/activity_sound_manager.hpp"
 #include "audio/mount_sound_manager.hpp"
+#include "audio/npc_voice_manager.hpp"
 #include <GL/glew.h>
 #include <glm/gtc/matrix_transform.hpp>
 #include <glm/gtx/euler_angles.hpp>
@@ -342,6 +343,7 @@ bool Renderer::initialize(core::Window* win) {
     footstepManager = std::make_unique<audio::FootstepManager>();
     activitySoundManager = std::make_unique<audio::ActivitySoundManager>();
     mountSoundManager = std::make_unique<audio::MountSoundManager>();
+    npcVoiceManager = std::make_unique<audio::NpcVoiceManager>();
 
     // Underwater full-screen tint overlay (applies to all world geometry).
     underwaterOverlayShader = std::make_unique<Shader>();
@@ -2132,6 +2134,12 @@ bool Renderer::loadTerrainArea(const std::string& mapName, int centerX, int cent
             activitySoundManager->initialize(cachedAssetManager);
         }
     }
+    if (mountSoundManager && cachedAssetManager) {
+        mountSoundManager->initialize(cachedAssetManager);
+    }
+    if (npcVoiceManager && cachedAssetManager) {
+        npcVoiceManager->initialize(cachedAssetManager);
+    }
 
     // Wire WMO, M2, and water renderer to camera controller
     if (cameraController && wmoRenderer) {