Implement immediate settings application and fix escape menu behavior

Settings Changes:
- All settings now apply immediately without Apply button
- Each slider/checkbox instantly updates the game state and saves
- Escape key closes settings window if open (no longer shows escape menu behind it)
- Restore Defaults buttons now also apply settings immediately

Audio Changes:
- Increased NPC voice volume from 0.6 to 1.0 (60% to 100% base volume)
- Helper lambda in Audio tab for efficient volume application
- Master volume multiplier applied to all audio systems in real-time

UX Improvements:
- Removed redundant Apply button
- Settings save automatically on every change
- More intuitive settings flow - see changes instantly
- Cleaner escape key handling priority

src/audio/npc_voice_manager.cpp

@@ -306,7 +306,7 @@ void NpcVoiceManager::playSound(uint64_t npcGuid, VoiceType voiceType, SoundCate
     bool success = AudioEngine::instance().playSound3D(
         sample.data,
         position,
-        0.6f * volumeScale_,
+        1.0f * volumeScale_,
         pitchDist(rng_),
         60.0f
     );