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/audio/npc_voice_manager.hpp

@@ -6,6 +6,7 @@
 #include <cstdint>
 #include <random>
 #include <chrono>
+#include <glm/glm.hpp>
 
 namespace wowee {
 namespace pipeline { class AssetManager; }