[Option B] Create CoreAudioHardwareProvider implementation

[danieljsinclair]

Issue

Create CoreAudioHardwareProvider implementing IAudioHardwareProvider for macOS platform.

Background

Current AudioPlayer uses CoreAudio AudioUnit directly. We need to extract platform-specific code into a dedicated provider class.

Goal

Create CoreAudioHardwareProvider that:

• Implements IAudioHardwareProvider interface
• Uses CoreAudio AudioUnit for audio playback on macOS
• Provides clean platform abstraction
• Supports callback registration for audio rendering

Implementation Plan

1. Create CoreAudioHardwareProvider.h/cpp implementing IAudioHardwareProvider
2. Extract AudioUnit setup from AudioPlayer::setupAudioUnit()
3. Extract AudioUnit callback from AudioPlayer::audioUnitCallback()
4. Implement all IAudioHardwareProvider methods
5. Manage AudioUnit lifecycle internally

Acceptance Criteria

1. CoreAudioHardwareProvider.h/cpp created implementing IAudioHardwareProvider
2. Initializes AudioUnit with specified sample rate and buffer size
3. Supports start/stop playback
4. Supports volume control
5. Supports audio callback registration
6. All existing AudioPlayer tests pass
7. Clean build with no warnings

Testing

• Unit tests for CoreAudioHardwareProvider
• Integration tests with AudioPlayer
• All smoke tests pass
• No behavioral changes (audio sounds identical)

Dependencies

• Remove/accurately document SilentRenderer in architecture docs #9: Create IAudioHardwareProvider interface

Related Issues

• Clarify FillSilence location in architecture documentation #10: Consolidate ThreadedStrategy implementation
• Document actual pull model architecture (modes/renderers/factories) #11: Consolidate SyncPullStrategy implementation
• Archive and reference historical investigation docs #14: Update CLIMain wiring for IAudioStrategy