Wire SMSG_PLAY_SOUND to AudioEngine via SoundEntries.dbc lookup

Add PlaySoundCallback to GameHandler (same pattern as PlayMusicCallback).
When SMSG_PLAY_SOUND arrives, resolve the soundId through SoundEntries.dbc
(fields 3-12 = files, field 23 = DirectoryBase) and play the first found
file as a 2-D sound effect via AudioEngine::playSound2D(). Previously the
opcode was parsed and dropped.

src/game/game_handler.cpp

@@ -3041,6 +3041,7 @@ void GameHandler::handlePacket(network::Packet& packet) {
             if (packet.getSize() - packet.getReadPos() >= 4) {
                 uint32_t soundId = packet.readUInt32();
                 LOG_DEBUG("SMSG_PLAY_SOUND id=", soundId);
+                if (playSoundCallback_) playSoundCallback_(soundId);
             }
             break;