Add configurable auto-pause delays for YouTube video compatibility

## Summary Implements user-configurable delays for auto-pause functionality to resolve issues where brief speaker pauses caused unwanted music resumption during YouTube videos. Fixes #203 ## Changes - **New preferences UI** with logarithmic sliders for fine control at small values - **Configurable delays**: 0ms (disabled) to 10000ms for both pause and unpause delays - **Default values**: 1500ms pause delay, 3500ms max unpause delay - **Persistent storage** via NSUserDefaults with proper validation - **Zero-delay support** for immediate pause/unpause behavior ## Test plan - [x] Build completes successfully - [x] UI displays correctly in preferences menu - [x] Sliders provide logarithmic scaling for fine control - [x] Zero delays disable respective functionality - [x] Settings persist across app restarts - [x] YouTube video pause issue resolved ## Technical Details - Added `pauseDelayMS` and `maxUnpauseDelayMS` properties to `BGMUserDefaults` - Modified `BGMAutoPauseMusic` to use configurable delays instead of hardcoded constants - Created new preferences UI with logarithmic sliders for better UX at small values - Proper validation and clamping of delay values (0-10000ms range) - Zero-delay handling for immediate behavior when delays are disabled