Add mute button and original soundtrack toggle

- Mute button: small [M] button alongside minimap zoom controls, turns red when active; directly sets AudioEngine master volume to 0, restores on unmute; persists in settings.cfg
- Original Soundtrack: checkbox in Settings > Audio that controls whether custom original music tracks (file: prefix) are included in zone music rotation; when disabled, only WoW MPQ tracks play; persists in settings.cfg
- ZoneManager.getRandomMusic() now filters file: paths when OST is disabled, falling back to full list if zone has no non-file tracks

include/rendering/renderer.hpp

@@ -155,6 +155,7 @@ public:
     double getLastWMORenderMs() const { return lastWMORenderMs; }
     double getLastM2RenderMs() const { return lastM2RenderMs; }
     audio::MusicManager* getMusicManager() { return musicManager.get(); }
+    game::ZoneManager* getZoneManager() { return zoneManager.get(); }
     audio::FootstepManager* getFootstepManager() { return footstepManager.get(); }
     audio::ActivitySoundManager* getActivitySoundManager() { return activitySoundManager.get(); }
     audio::MountSoundManager* getMountSoundManager() { return mountSoundManager.get(); }