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.

include/rendering/renderer.hpp

@@ -8,7 +8,7 @@
 namespace wowee {
 namespace core { class Window; }
 namespace game { class World; class ZoneManager; }
-namespace audio { class MusicManager; class FootstepManager; class ActivitySoundManager; class MountSoundManager; enum class FootstepSurface : uint8_t; }
+namespace audio { class MusicManager; class FootstepManager; class ActivitySoundManager; class MountSoundManager; class NpcVoiceManager; enum class FootstepSurface : uint8_t; enum class VoiceType; }
 namespace pipeline { class AssetManager; }
 
 namespace rendering {
@@ -149,6 +149,7 @@ public:
     audio::FootstepManager* getFootstepManager() { return footstepManager.get(); }
     audio::ActivitySoundManager* getActivitySoundManager() { return activitySoundManager.get(); }
     audio::MountSoundManager* getMountSoundManager() { return mountSoundManager.get(); }
+    audio::NpcVoiceManager* getNpcVoiceManager() { return npcVoiceManager.get(); }
 
 private:
     core::Window* window = nullptr;
@@ -175,6 +176,7 @@ private:
     std::unique_ptr<audio::FootstepManager> footstepManager;
     std::unique_ptr<audio::ActivitySoundManager> activitySoundManager;
     std::unique_ptr<audio::MountSoundManager> mountSoundManager;
+    std::unique_ptr<audio::NpcVoiceManager> npcVoiceManager;
     std::unique_ptr<game::ZoneManager> zoneManager;
     std::unique_ptr<Shader> underwaterOverlayShader;
     uint32_t underwaterOverlayVAO = 0;