fix: add share sheet button

[destucr]

🎯 Summary

Added a share button to the Live Listen playback interface, allowing users to easily share their recorded heartbeat audio files.

✨ Features/Changes

• Added a share button (with square.and.arrow.up icon) that appears in the top-right corner during playback mode
• Share button is conditionally visible only when in playback mode
• Integrated with existing share sheet functionality for exporting audio recordings

📁 Files Changed

• Tiny/Features/LiveListen/Views/OrbLiveListenView.swift - Added share button UI component in topControlsView with conditional rendering based on isPlaybackMode

🔧 Usage Examples (if applicable)

// Share button appears in playback mode
if viewModel.isPlaybackMode {
    Button(action: { viewModel.showShareSheet = true }) {
        Image(systemName: "square.and.arrow.up")
            .font(.system(size: 22, weight: .semibold))
            .foregroundColor(.white)
            .frame(width: 50, height: 50)
    }
    .glassEffect(.clear)
}

🧪 Testing Scenarios

Share Button Visibility:

• ✅ Share button is hidden in listening mode
• ✅ Share button appears in top-right corner when in playback mode
• ✅ Tapping share button opens the native share sheet
• ✅ Share sheet contains the last recorded audio file URL