Place screenshot PNGs referenced by the root README here (~800px wide):

- `hero.png` — wide shot: the pet on the desktop with a couple of session bubbles
- `pet-overlay.png` — the pet reacting to the highest-priority session
- `session-bubbles.png` — bubbles expanded, showing per-session status icons
- `folder-collapsed.png` — bubbles folded away beside the pet
- `tray-menu.png` — the tray menu (show/hide, pets, reset position, Quit)
