Adds support for capturing the frontmost window of the frontmost application
instead of falling back to screen capture mode.
Changes:
- Added 'frontmost' case to CaptureMode enum in Swift CLI
- Implemented captureFrontmostWindow() method using NSWorkspace.shared.frontmostApplication
- Updated TypeScript to use --mode frontmost instead of defaulting to screen mode
- Added comprehensive test coverage for frontmost functionality
- Updated existing tests to reflect new behavior
The frontmost mode now:
1. Detects the currently active application
2. Captures only its frontmost window (index 0)
3. Returns a single image file with proper metadata
🤖 Generated with [Claude Code](https://claude.ai/code)
Co-Authored-By: Claude <noreply@anthropic.com>
