Add file type icons instead of SF Symbols

[ringo380]

Description

Use actual file type icons (from LaunchServices) instead of generic SF Symbols for better file recognition.

Current Behavior

All files show generic document/folder SF Symbols colored by extension.

Proposed Behavior

• Use NSWorkspace.icon(forFile:) for actual file icons
• Fall back to SF Symbols if icon unavailable
• Cache icons for performance

Benefits

• Better visual recognition
• Matches Finder appearance
• Shows app-specific icons