Redesign toast UX: compact layout, progress bar, title-only mode ...

- Replace heavy colored header strip with inline icon+title header
- Add thin bottom progress bar showing remaining lifetime
- Support title-only compact single-line toasts (no text = no body padding)
- Increase tinted background opacity from 0.06 to 0.18 for visibility
- Fix vanilla toast defaults: all variants now use lifetime=4000, alone=true
- Add demo buttons for title-only variants in both vanilla and Vue demos
- Remove hover effect from toast close button
- Adjust close button position (top: 5px) and progress bar margin (1px)

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

Polish cards lists and toasts

Modernize Sass build pipeline

Add navigation overlays components

Scaffold GNexus UI kit