Add a single toggle switch to enable/disable sound effects in the Audio settings. This provides a simpler alternative to full sound customization while covering the most common use case. - Add sound_effects.enabled config option (default: true) - Add toggle switch in Audio settings tab - Add helper methods to ConfigManager - Update play_*_sound() to check enabled state - Add tests for the new functionality Closes #283 Ultraworked with [Sisyphus](https://github.com/code-yeongyu/oh-my-opencode) Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>