docs: turn the README demo into a product walkthrough

[xand0dev]

Summary

• replace the ambiguous hover loop with an 8.4-second live product walkthrough
• present the real app on a graphite product stage so the black panel silhouette, border, and shadow remain visible
• show the actual Music, Focus Timer, and Translate panes with synchronized captions
• explain the walkthrough in both English and Ukrainian README files

Why

The previous black-on-black loop did not communicate the product boundaries or tell a useful feature story. This version makes the interaction and the three representative workflows legible at GitHub README size.

Validation

• inspected a contact sheet across the full animation timeline
• verified the GIF as 1068×450, 8.4 seconds, and 604 KB
• ran git diff main...HEAD --check
• rebuilt the normal release app after removing the temporary capture-only storyboard hook