Audit Fixes & Usability Improvements

Bug Fixes

• Search filter in update mode - Search now correctly hides non-installed apps when in update view
• Stdout deadlock - Async stdout reading prevents hangs on large winget output
• Update detection - Added "Successfully updated" to success pattern matching
• Duplicate BorderBrush - Removed redundant property assignment in category builder

Usability Improvements

• Update mode toolbar - Irrelevant buttons (groups, export, import, copy) are hidden when in update view
• Back to Install - UpdateAll button toggles between modes for easy navigation
• Paired Select/Deselect All - Both buttons work on visible apps in both install and update modes
• Auto-restore - Install view automatically restores after update batch completes
• Empty categories hidden - Categories with no installed apps are collapsed in update view
• Search cleared on exit - Search box resets when leaving update mode
• Delete group - Immediate action without confirmation dialog
• Visible count - Shows correct totals when switching modes