fix: clean up modes, remove overlay, fix IZUI navigation stack
- Remove settings mode and minor modes from codebase
- Clean up vestigial overlay references (renamed to page:show-navbar)
- Filter peek:// URLs from groups UI (only show http/https)
- Fix IZUI stack navigation with targeted focus requests
- Windows now track their ID and parent ID
- Focus requests include target window ID
- Only respond if we're the target or sender is in our nav stack